I go to the pet store and get a 30-40 lb. bag of ground walnut hulls. They sell it for lining the bottom of bird cages.
I put that in my cleaner and use Dillon Rapid Polish and run it for an hour or so to get the cleaner/polish mixed into the media.
Tumble the cases for an hour or two and you are good to go.
You can buy media at most any Sportsman, Cabelas or Bass Pro, but you will pay through the nose for it.
I get mine at PetSmart and save some money and I am getting about 40 lbs at a time rather than the measly jar at the LGS.