Well, according to this (http://www.unibrite.com/PL_dENTAL.htm
), you can buy 50 lbs of silicon carbide for $87.40 (the black variety. The green costs much more, for some reason). I also found this, but no prices: http://www.alphamaterials.com/silicon_carbide.htm
. Silicon carbide bricks are sold as kiln furniture, so they're fairly common.