I buy my foam from Home Depot, because I know their source. Most foam manufacturers will have a minimum invoice amount.

The big drawback to building supply stores is that you do not always know what you are getting. For our use we need 1 lb. density, virgin ESP foam. Some of the ESP foam is not virgin foam and has recycled foam in it. This is fine for insulation but not so good for us. Recycled foam will have hard beads in it. When cutting, the wire will hang up on these beads and dwell for a while. The result is ridges along the core. You do not get this with virgin Foam.

Ed S