Foam for sump

[Rikko]

LFS/garden center pond filter media usually comes in 12"x12" sheets or sometimes on 36" rolls and you can cut your own. There's a few types of coarseness - you could probably find something close to what you want.
Beyond that, I found some stuff at a foam shop but it was ungodly expensive.

I also remember a customer once said he used the filter material from a furnace air filter.. It was a FW application but I suppose that stuff is safe.