There is a 35mm film back for a Bronica 6x6 camera; when I first found out about it, I envisioned a back that would let you shoot a whole roll of little square frames on 35mm film, and was sorely disappointed when I realized that it just shoots regular 35mm format. I like composing photos in a square frame. The suggestion to “just crop it” doesn’t cut any ice with me; I want the photo to be a square from the moment I frame it with my eye to the moment it’s developed on the film.
Are there cameras or camera backs that allow you to shoot a square frame, with a square viewfinder, on 35mm film?