There's a place in Denver that sells it by the "Bun" which is something like 12" x 42" x 48". They can then slice that Bun any long way you want. (De-skin, 1/4", 1/2", 1", 2", 3", 6", whatever- sliced like bread), but the minimum buy is one Bun's worth and it normally has a skin all the way around the block (foam skin does not glue well to plastic).
When I did buying for a kayak shop, we bought 2 Buns a year and had them cut to out thicknesses. Then we would cut them down the rest of the way (12" Squares) for resale. Still not much of a profit. That foam is pricey.
If you did a search for Denver Foam Wholesalers you'll most likely find them.
I love to dance, but who needs the music- It throws me off.