You can make some using ammonium nitrate found in instant cold packs and magnesium.
whats the name of the cold pack and now the wheel that spins the rock tumbler broke do you know how to fix that????
pretty much any kind of instant could pack will work and I need to see a picture of the rock tumbler to help with that.
the first one shows the driveshaft with the thingy that was on it that helped it spin the 2nd one is the thingy that helped it spin
Sorry I can't help you there your probably best buying a new rock tumbler.
Forgot to add this link http://www.youtube.com/watch?v=4D1bNefVn28&feature=related also note that you can substitute potassium nitrate for ammonium nitrate.