There is already an excellent documentary out there which you may want to look at as research. An English reporter spent several days talking to members of the New York scene - though it was mostly professional Dommes. The Dommes were fine to have their faces revealed but most of the clients chose anonymity. It was very interesting to watch. I have a copy somewhere but it is on VCR.

There are places out there where you can advertise for models who can come and enact realistic scenes for you but that won't be a 'documentary'. I am sure there are also lifestylers out there who will 'out' themselves for you.