Where Can I Get Good Slate?

[Luketendo]

I want some slate suitable for aquarium use, it needs to be quite thin, not extremely small and big enough to make a cave or tunnel out of.

Does anyone know where I could get slate like this?

 

[Esfa]

I want some slate suitable for aquarium use, it needs to be quite thin, not extremely small and big enough to make a cave or tunnel out of.

Does anyone know where I could get slate like this?

look at your lfs? garden center?