I got a semi-trailer load of pink & green from a const. site about 10 years ago. I still have some of it leftover. Now, I use cellotex ceiling tiles for all my mountain scenes
& patching plaster over aluminum screen wire for larger mountains.
I went to the const. site & talked to the foreman & told him I would come by everyday
& clean up the insulation that was outside the building. He said "Great". It was costing
them a lot to haul all the scrap to the dump. I also got all the elect. conduit scrap. plywood scrap & a 5 gal. bucket of self tapping sheet metal screws. Also, got about 500 ft. of scrap 14, 16, & 12 ga. wire.
Wherever their is a concrete block building being covered w/brick, you can usually find the dense foam. You can also get it in yellow, green, pink & blue. The colors are the density of the foam.