: I'm looking for sources for rigid polyurethane (or comparable) foam for
: prototype/model/plug work . . .

Why not polystyrene foam? Just about any Home Depot or similar big box home center will stock 4x8 sheets at very reasonable pices. 3/4 inch is about $10 to $12 a sheet. Standard sizes go to 2 inches thick, at about $30 a sheet. You get your choice of pink or sometimes blue. if you want another color, use paint.

No shipping fees. If 4x8 is too big to fit in your car, tie it to the roof, or bring a knife or handsaw with you and hack the big sheets down to size in the parking lot.

Sculpt the stuff with a hot wire, blowtorch, beltsander or power planer then use a finer grade of sandpaper to get a fairly smooth surface, which you can fill or paint with an epoxy-based resin to achieve a very smooth surface to use this as a plug.

Just a thought.

PGJ