Depends on what you wanna do. If you wanna edit a documentary, you'd probably be more of an assistant as most doc filmmakers have editing chops and know what they want. It's only when you get into the real high end stuff, where the budgets can afford real post production support, that things change.
I'm a documentary filmmaker, I've been specializing in the field for nearly my entire life, mostly because I like telling stories and it takes years to tell stories in narrative forum. I've found the documentary process very entertaining and pretty fun, especially when I'm given a challenge of telling a story in limited amount of shooting and post time.
I'm always prepping, shooting and editing a documentary. Right this second I'm finishing a cut of one for a friend, I'm shooting two (both on film) and I'm prepping another that will be shot next year. I find the process to be a 360 degree turn from conventional narrative, commercial/industrial work. Like most doc filmmakers, I'm a one man band with zero crew. Yes I do have a producer, but she doesn't do much besides setup interviews and help schedule things. This is pretty typical for documentary filmmakers, they run the camera, they even setup the lighting/mic's and such. You've gotta be super technical and understand your limitations on set, like what you can and can't bring with you etc. I have two very nice travel kits, one digital and one film, both fit into super small backpacks. Nobody would know I was off shooting a documentary film. You can see some of the highlights in my cinematography.com blog: http://www.cinematog...showtopic=76110
Anyway, I'd just go out and make my own doc really. I think trying to cling onto someone else isn't the right idea unless you just wanna shoot and/or edit, in which case, it's only about your demo reel at that point.
[shamless_plug] Here is a link for a teaser of my upcoming doc about shooting on film. Sadly, I had a major setback recently where two of my interviewee's backed out due to financial constraints and they aren't shooting their movies at all now. So I need to find a few more people to interview on this subject and shoot BTS. . [/shameless_plug]