While I have no definate information on the subject of the folding stock MAS-36, they were issued and used in combat. Some things do get produced, issued but sit out most of their lives in a box somewhere, only I don't think that was one of them. I doubt they were produced in great numbers. But for that matter, how many M1A1 carbines were made out of the total number of carbines?
Another similiar weapon was the Mosin-Nagant cavalry carbine produced for the Finnish Army. They manufactured it only for the use of mounted units, so not very many were made but they were "regularly" issued. They would be rare.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.