As far as I know Kodak is still producing 10 inch Cirkut film. I have a fair supply (over 2,000 feet of Portra 160) but 400 is also available.
Photo sales of large groups is usually very good. I have had more than several where more prints were sold than there were people in the photo. The photos can be produced for less than $8 each and sell for $45 - $65 each depending on the length although I also sell smaller groups or school photos for as low as $20 each again, it's a volume thing that makes the money.
As far as someone running to both sides of the photo, I don't advertise that it is possible but don't mind if they do it. I usually tell them it's only right that they buy two copies.
Everybody likes having their photo taken with a camera that is very old and LOOKS like how a camera should look, you know what I mean, a big box with bellows, wood tripod, bits of brass showing, and always the black focusing cloth waving. The big cameras still have magic.
Ron in Alaska