That URL hung on me, but this one takes me to the Silverstone acoustic foam.
You can get plasticine and stiff felt at Michael's.
Awesome, so you think it should work? I was planning on getting some stuff from Michael's too, plasticine should be pretty easy and cheap to get my hands on.
I do have some Sculpey bake-clay...which seems to be pretty much plasticine that you can bake to harden. Wonder if that'd work? A bit expensive compared to normal plasticine but I do have some sitting around and probably won't use it for anything else for awhile...