As you only want the bottom you can look at the price list for the Bessa R2S/C case, Black for $40 (about 5/8 of the way down the page).
There was an RFF half case that the head bartender had a while back that I can not find anything about now. Drop him an email and you might find something.
Keep in mind, any case that fits a Nikon FM10, Olympus OM2000 and several other cameras from Cosina will fit the bottom of the R very well.
I had one, but sold it some time ago for a profit of $9 I think (I paid a buck for it).
B2 (;->