Helen,
Mamiya had a rangefinder called the "Magazine 35" which had interchangeable backs, but it was a fixed-lens as far as I know. I don't even know if it was a leaf-shutter, although that was the era for them and Mamiya did make leaf-shutter rangefinders.
I'm sure you already know about this website, but for others who might be interested:
Mamiya Rangefinders
I'm trying to think of other interchangeable lens rangefinders - there were a bunch, but I can't recall them all right now...
* Braun Paxette series. 39mm screw mount, but not Leica.
* Diax Ia, IIa, IIb. Sort of a weird outer-rim screw mount.
* Voigtlander Prominent.
* Kodak Retina (not fully interchangeable, lens fronts only), except for Retina IIIS, which was a complete interchangeable lens, leaf-shuttered camera.
* Lord Lordomat and perhaps a few others.
* Regula King Regula and perhaps a few others.
* Minolta Super-A. Never seen one, just heard of them.
* DeJur III (could be wrong on the model number).
* Wittnauer Professional. Used the Compur lens mount - this was interesting because Kodak used a similar but slightly modified lens mount for the Retina IIIS and leaf-shuttered SLRs, and Voigtlander used it also for the Vitessa T (same as the Vitessa "barndoor" cameras, but with interchangeable lenses and no barn doors).
* As above, the Voigtlander Vitessa T.
These are just the ones I can remember off the top of my head. I love collecting these types of cameras. One problem with all of them is that with an exposed leaf-shutter lens, there is more potential of time-induced damage due to exposure to the elements than perhaps there is with fixed-lens leaf-shutter rangefinders.
Best Regards,
Bill Mattocks