There are still caches of frozen Super 8mm Sound film in the hands of many filmmaking enthusiasts. I would image film will still show up for processing many years from now. The cartridges are KODAK's design, and while minor variations of it were made by both AGFA in Germany and Sakura film in Japan (Konishhiroku)....and under the other store brand names; only the KODAK cartridge was robust and allowed lap dissolve functions to work the best. The design was used under license to KODAK, and those companies that sold cartridges with KODAK made film used KODAK cartridges. Getting new cartridges made these days would be very costly. KODAK does sell new empty loadable SILENT cartridges, but long discontinued the SOUND ones. That being said, used cartridges can be reused many times. I conducted some tests years ago, refilling two cartridges a dozen times each or so, and they ran fine, and I still have those two test cartridges in my collection and they could still be used. So a lot to say for what was supposed to be a disposable piece of plastic after it was used for some 3 minutes.
Using a sound film camera in Super 8mm is a fun experience. Camera noise, well, if you don't apply professional filmmaking technique in 16mm or 35mm, you'll also have camera noise. A little care, using a long microphone cord, a directional microphone, or a wireless microphone, careful placement of the camera if indoors, blimping if doable, will add to gaining fine sound. The original ELMO demonstration film showing the Stereophonic capability of Super 8mm film, that came with their flagship projector, the GS-1200, showed how wonderful sound can be even at 18fps! I got great sound even on my first sound camera, a SEARS badged Chinon made 195XL which only had auto exposure and ALC audio recording. For family and fun goofing about films, yes, sometimes you do hear the camera noise, but so what, you could also hear the zoom motor or fingers fumbling on the buttons of many video cameras, or the sound of finger moving on the body of the video cameras or digital cameras of today. It's part of the ambience of shooting live-sound when doing such spontaneous filming.
Anyone wanting the best results, will use proper technique for a production where the results should be higher. For that matter, what about the projector noise when projecting a film.....how many build their own projector booth? There are some fans that do, others place it far enough away from their audience, but not all. And for silent films, you'll often hear the projector, it's part of the experience. In fact, some places that offer film transfers, will add in projector noise if desired, instead of some bland elevator music soundtrack.
The BOLEX 5120 was made by Chinon Industries along with the majority of cameras they made for others. Some Super 8mm Sound cameras were quieter than others, and the NIZO models were the best for quiet. That being said, I have gotten and still get great results from my SANKYO XL-620 and some of the other sound cameras I have. BAUER also made some very good ones, even their rebadged PORST ones are fine. The older GAF SS models I have made by Chinon will probably last for many years, with only the drivebelt going bad (the weak link in any belt-driven capstan audio recording mechanism).
I've been experimenting with films bought off eBay and those that often come with older cameras one finds either on eBay or yard sales, that still have old film in them. These old sound films, poorly stored over the decades of time, will more than likely not yield decent color, since it shifts to mostly green with the old EKTACHROME films.......and even very old KODACHROME which can only be done as B&W now, will also suffer from age. The film fog from age affects both film types, as well as any old AGFACHROME, AGFAMOVIECHROME, M-CHROME-BOOTS-PORST etc(Agfa made films and others), so really they are best processed as Black & White Negative. But even so, you'll have a B&W neg with a magnetic audio track, in synch, for transfer to video. Sometimes, they can even be done as reversal, but not well.
Old Sound film can be used to test a camera's sound recording mechanism. With opening of the cartridge and reloading, it can be used over and over again for such testing; using different microphones, cables, techiques etc BEFORE you use any good film. Just erase the audio on the old film with a degauzer before reloading the cartridge for the next test. Film removed from such old cartridges can also be used to practice recording technique on a Super 8 Sound Projector, BEFORE ever doing so on a film you shot. All this can help avoid mistakes.
When my first child was born, I shot the birthing experience (tastefully) in the hospital on Super 8mm Ektachrome 160A Sound film, in full CinemaScope as well, and if you were to see this film, you would say, wow, that's cool. So is the camera noise in the background, as are the other noises, nurses with instruments, the heartrate monitor machine etc. Believe me, I wasn't concerned in the least about any camera noise being picked up in the tiled serile room with lousy accoustics. Between takes, I held my wife's hand and helped out where I could. It was not a professional production, but a family event, just like many things we photograph and record in life. If it had been a professional production of a birthing event, I would've used other techniques, since I would not have been so personally involved.
That Revue SuperChrome clip is precious! The blotches that you see at times is the darn remjet that AGFA used, it's rubbery coating that is nearly impossible to completely remove when processing such now old films. In that respect, the EKTACHROME 160A films are better, but even so, sometimes small minute traces of the remjet might show. With manual film processing, we don't have the dedicated buffer rollers with rinsing jets as the large KODAK EM-26 film processors had. I have processed old film that looks mostly green, and it's still enjoyed by those that are in it when projected. It can be made B&W or Sepia when put into a video format later on if desired.
So, yes, you can shoot Super 8mm Sound film in a sound camera and get great results if you are careful and truly wonderful results if you use professional techniques. If just shooting family or personal events, or even artistic stuff, any noise might not be that bad. I shot a field of wheat moving in the light breeze years ago on vacation and the camera mic did a great job and even picked up the distant sound of a train, yet no camera noise. That was outdoors of course, without a wall to throw back the sound to the mic of the camera as it could indoors. Processing is available for virtually any film ever made. I process most anything here, except Color Neg which I'm experimenting with again later this year to see if it's viable. In the past, the handful of labs that sell and deal with Color Neg films in Super 8mm, have that market. Pro8mm state they can process EM-26 films for $90 each 50ft cartridge, Spectra state they do it for $65 each 50ft cartridge, Film Rescue in Canada do it for around $44 each, and the Super 8 Lab in the Netherlands also was doing it, in addition to myself here in Plattsburgh, New York at much less. Anyhow, I suggest asking each of the labs that offer such processing what their rates are, turnaround times etc, and then figure out whether or not you think it's worth it to you. I think ideally, everyone that ever shoots any Super 8mm film, should experience shooting at least one roll of sound film, while it can still be found out there somewhere. Or via FUJI's Single-8 system which also offered Sound Film and Sound Cameras.
Lastly, as for making new SOUND film, it is an expensive proposition, which I have experimented with over the past several years. The gentleman in Spain who has a camera shop has made a few sound striped films available and might still be doing so. It is not cheap, and as with anything done on an ultra tiny scale by one person would be quite expensive. I had done up some B&W Sound film some years back and had thought of offering that. But from a practical cost standpoint as well as labor-intensiveness, it is really only doable with a single main track on the film (not with both sound tracks as when KODAK and other companies were mass producing it via large machines). The cost was easily going to be upwards of $55 to $70 each 50ft cartridge and that just seems too expensive to me.....especially when there was and most likely still is, caches of Sound film out there in the hands of filmmakers freezers to still use. i suppose, in the end, should all Color Reversal chemistry cease, any remaining film can still be processed as B&W, since those chemistries can be mixed up to formula from readily available raw chemicals.
Well, I've rambled on enough, hope I haven't put most of you to sleep!