The "Focusing and Lens Head Adapters" were made for the 100mm f3.5 chrome (Focusing Adapter RB) and for 85mm f1.9 chrome, 100mm f2.0 black, and 135mm f3.5 chrome (Focusing Adapter RA). Each lens head adapter is unique to the lens head. So there were four lens head adapters and two focusing mounts.
Unfortunately the focusing adapter sets were designed for Canonflex SLR so the lenses won't focus to infinity on MB2. The Lens Head Adapters for the RA mount fit on the Bellows R, without the RA mount. But even then they won't focus to infinity on MB2. The Lens Head Adapter for the RB mount doesn't seem to fit anything other than the RB mount.
Peter Kitchingman's outstanding book "Canon M39 Rangefinder Lenses 1939 - 1971" suggests that 9824 units of the 135M lens may have been made based on serial number range. The book also suggests 2082 units of the 200M lens may have been made. If this were so, the lenses would be easy to find.
I posted a thread on the Canon Rangefinder subforum on 15 March 2014, titled "What happened to old Canon Big Glass". In the thread I suggested that the 135 and 200 lenses were numbered in the same serial number sequences with the R and FL lenses.
What still strikes me as odd is that the MB2 is relatively easy to find, but all the lenses are rare. It has taken me years to acquire a full set of MB1 and MB2 lenses and the RA and RB focusing adapters.
Right now there is a 400mm 4.5 lens and a 800mm f8.0 lens on e-bay. The 800mm lens is way over priced and has been heavily modified so it is not even collectible. The 400mm lens is merely over priced. The only difference between the R-set and S-set (also referred to as Model 2) is the case. The lens head / lens support / intermediate tube / bellows R build up for a complete, usable lens is exactly the same for MB2 and Canonflex.
