Wiki says the 35mm film back "never materialized", do you know something? (You were a tech rep for them ; ) Should I start looking?
The Bronica GS-1 35mm backs were never made, except some undocumented reports out of Asia.
GS-1 makes film backs in 6x7, 6x6 and 6x4.5 and Polaroid.
The GS-1 6x7cm (2 1⁄4 x 2 3⁄4˝) camera offers high
precision and creative versatility.
At only four pounds
with its standard lens, it is far lighter and more
compact than its 6x7cm SLR rivals. It can be handheld
on location as well as in the studio. And with
Bronica’s exclusive backs, it can also shoot 6x6cm,
6x4.5cm and Polaroid. With the optional AE Prism
or AE Rotary Prism finder, aperture priority auto-exposure
with TTL-metering is possible. The GS-1 also has
OTF TTL flash metering when used with a dedicated
flash. GS-1 - a lot of camera for the money.
The features are:
■ Extended internal functions for professional needs
■
Smallest and lightest 6x7” SLR camera
■ Interchangeable finder system
■ Mirror Lock up mechanism
■ Large studio camera with the portability of a 35mm
■ Unique electronically controlled Seiko lens shutter
■ TTL flash capability with speed grip
■ Multi-format system camera - 4 types for different formats