Accurate Litho There is a company called Katz that sells it. They used to sell the stock in large sheets, not just coasters. Not sure if they still do. They have a coaster reseller program though.
katzamericas.com
Careful though, it really needs to be die cut. Like on a clamshell die cutter. If you cut that stuff on something like a zund, it chews through carbide blades too fast to be cost effective.
We'll actually run
coaster out of 3mm PVC. It's not absorbent, and is just a little more money, but it's a nice product. Just order a custom size from us.
Good luck!