I bought some key touches once on EBay, to replace the awful cheap plastic things on my awful cheap soprano. They were “stone”, I suspect they were actually dust from grinding decorative stone bound together with epoxy. At the very least there was some kind of binder in them.
In any case, they feel very good, not as good as real MOP, but a serious step above the plastic crap that was in there. And they were not expensive - $10 or $15 for a full set. I think Cannonball saxes use a similar material for their stone touches.