I buy them at Academy Sports. I would think that any sporting goods store that sells pitching machines would have them. So far, have only used .22LR and 9mm on them and it hardly damages them at all. Made with some kind of polyurethane I think.
I found them on Amazon. Price was good, but sold in lots of 12.
Looks like Academy Sports is only in Tenn.
I’ll check next time I go into the city. Something bigger than what I’m using would be nice for the handguns.