They will not sell you any. Seriously......unfortunately, this is a lost-cause venture. A couple years ago, I said, "No, I will make this happen." Well......I'm telling you......its not going to happen. :-\
Not trying to be negative, just trying to save you some time.
Poor Valley may be able to shed some light on some more specifics to this. There's a guy that has the patent on ceramic bisque for use in turkey calls, and you can buy in to it, but I know Poor Valley tested some, and did not like them at all compared to slate and glass.
Parker