Many pet stores carry ground corncob media for small pet bedding. It is usually a little coarser than most normal tumbling media but it should still be perfect for tumbling cases (and not get stuck in flash holes). Prices at my local Petsmart were about 2/3 of the shooting stuff. For ground walnut shells many pet stores sell it in the same grit size as the shooting stuff as “lizard litter” or “bird cage litter.” The local price seems to be about a 30 percent cheaper than the shooting product.
You can also try your phone book’s yellow pages for an industrial abrasives dealer. While you’ll have to buy the corn cob or walnut media in 50 pound bags from them the price is usually about half (or less) of the price from firearms related sources, and it should keep you in clean tumbling media for the next several years. For an extra high polish add a small amount of non-ammonia containing automotive rubbing compound to the corn cob media and run your tumbler for a few minutes before adding the cases.
A word to the wise. If you share your home with furpeople keep your tumbling media covered or you may find some strange “cases” in it. Cats think its a dandy litter box filler.
Another case cleaning method that works well in rotary tumbler, like the 1-gallon Thumblers Tumblers, is to use the following media.
2 lb yellow or white corn meal
1 cup plain table salt
1/4 cup corn starch
5 or 6 pieces of scrap 2 x 2 or smaller wood cut into blocks
Add everything to the tumbler, close up the drum, and turn it on for a couple hours. Remove cases from tumbler, shake out the media from cases. You can blow them clean with an airgun or rinse them off if you like. The wooden blocks seems to knock the brass around and keeps media moving in and out of cases. They also seem to add a little extra friction to help polish and clean. Note that corn meal does not clog the flash holes, it’s dirt cheap, and lasts for hundreds of rounds!