Tom, There has to be some coal around Montrose? Hay Gulch Coal in Hesperus for sure, but that is a little far. If nothing else, post a "beg" for a small chunk on the Silverton Community FB page ... I'm sure that someone would mail you a piece to break up. I had a whole box of large chunks that I used for rubber molds but left it in Albuquerque years back. If you can't find any -- maybe experiment with some crushed plaster - painted?