He doesn't sell the foam through his site, but, I know he uses it in his new Matrix, so he's bound to have some scraps around - at least large enough for your case. Like I said ask him, and he should be able to help you.

You can get the foam (Ensolite) from the following source:
http://www.skandiaupholsterysupplies...ectGroup_ID=17

If you really have a hard time getting the mat, let me know, and I will cut you some.

I'll be ordering foam as well fairly soon, so I can get some extra if need be.