i have owned a rb67 system for a while and loooove it...as far as there being a 35mm back for it..there isnt one in production but i have heard of ppl who have modified old backs to be able to handle a 35mm film cartridge....

why would you want to shoot 35mm in a medium format when you can just use a 35mm slr....there rationale was just to get used to the system before investing the monies needed with 120/220