I need to replace the old foam and wonder if anyone knows who might sell that kind of stuff.

I don't know where to get the kind with the bumps, but one of the local sewing supply stores (they sell cloth, upholstery fabric, patterns, buttons, & etc) sells several different grades of foam (people who restore boats and cars buy it there).  They sell a very high density, stiff, dark grey foam in lots of different thicknesses.  This is exactly the same stuff found in custom electronic equipment cases.  I buy nylon strap and plastic quick release buckles there.

To find some one that sells foam, look up "Foam" or "Upholstery Supplies" in the yellow pages of a good sized city.  The Denver yellow pages has several listings.

Good luck.