Yes, it's an essential part of the camera kit. People might swap ground glasses over for different aspect ratios, but the camera viewfinder is essentially unusable without a ground glass.
Try to source a ground glass that will match the format and aspect ratio you want to film in, for example S16 1.78. Sometimes you can get multiple aspect ratios marked on one ground glass. You may need to just rent one from a rental house. Or contact the people you bought the camera from and demand the ground glass that it should have come with.
SR1 and 2 ground glasses will also fit your camera but are often marked for Standard 16, so make sure you get a S16 one if that's the format you want.
I don't know where you can buy them these days, try respected camera dealers like Visual Products or Gecko-Cam or even older established rental houses that had film cameras and are now offloading their film accessories. There used to be a company called Shurko that made and re-marked ground glasses, but I haven't used them for years.