I wanted two cheap pizza stones that I could double up and use to bake
bread and such. I've seen suggestions online to look into unglazed
quarry tile with some caveats. Most noteably, graphite is a bad idea
because it's radioactive--though I imagine that's not the least of it.

At the local Home Depot, they only had slate. It was very rough and
didn't seem suitable. Does anybody have a suggestion on a stone and of
any stores that might have it? I'm trying to get 15" tiles.