Slate source for calls?

My retired father has decided he wants to make a slate call. Where are you guys who make calls sourcing your slate? Used to you could get it from old roofs, but not too many around with slate anymore.

Brookside game calls

some on Ebay under turkey call

It's been awhile but I have ordered call supplies from this place. Was always happy with them.

https://www.shipleysoutdoors.com/game-call-supplies

grassycreekcalls.com

Thanks guys!