It is pricy, but available without special government contacts. Digi-key will sell a 5 inch by 7 inch piece, which is about 4/1000th thick for 84 bucks. It is about 1/3 the weight of aluminum for a given volume, survives insane heat (similar to a diamond), blocks heat through the thinnest dimension, but conducts heat end-to-end 3 times better than copper and as a plus, it levitates above a magnet. Wrapped around a gun, makes it invisible to metal detectors, a very exotic material. Larger sheets are available from the manufacturers, but the price scales up with the size.