I don't know if you consider it carving foam, but I've had very good luck with insulating foam (at least on the little N scale model RR I piddle with). It comes in blue, green and pink and in thickness's of 1/2 to 3 inches. Biggest problem is you have to buy a 4 ft by 8 ft piece. And carving or sanding can be a real thrill with it's demonstration of the properties of static electricity. Anyway, check out your local lumber yard or home improvement store (ie Lowe's or Home Depot)