Source for cobblestone-ish scene setter material?

Anybody know a place to get some? I want to fill in some gaps in my walls of the crypt and would like something that at least vaguely matches the cobblestone vacuform panels.

The panels I'm trying to match look very much liek these:

Cobblestone [VF-.030-HIPS-Cobblestone] - $38.75 : VacuFormStore - VacuForm Panels, Brick, Rock, Stone, Slate, Siding, Roofing, Bamboo, etc.

So far, the only stuff I've seen is cobblestone gossamer but it looks plain odd in the picture: Flame-Retardant Patterened Gossamer- by Shindigz