Go to Lowe's, Home Depot, National Welders or someplace like Tractor Supply or any metal working shop and they have them. Around here we refer to them as soap pencils. They are either round or flat in a metal case. Here is a link to a soapstone:
http://208.178.227.196/cgi-bin/nw/WService=nw/prodbrws.html?id=614104 Drew
