Who sells lead shot pellets to fill an equip.stand

How about copper BBs from WalMart?

If you can use steel in lieu of lead, you can get it from suppliers that supply sand blasting media. We use steel shot to treat aircraft parts and it would be a lot cheaper than 500 cans of bb's or whatever. I lot of guns now use steel shot as well due to enviornmental issues, so the lead may be hard to procure.
Good luck, John

Clay based Kitty Litter is widely used...........

A good option may be the stuff they use in those outdoor ashtrays in public places. It is denser than play sand.
However, is is around $15.00 per box and may get pricey
depending on how much you need.