As long as the stuff doesn't have an odor, I can't see why it wouldn't work fine.

It is similar to cat litter which has been used as a filler material for years. I would check to see which is the least expensive. It is a good suggestion, however, to combine two or three different materials in a fillable post. Lead shot, sand and litter are the most common and offer different damping abilities as the resonance hits each layer.

In what kind of store would you find the lead shot, and what size would you use?

Just about any good gun store would have lead shot. You can buy about as much as you want...bags and bags. I would go with small bird shot as opposed to the larger buck shot.

Folks,

I know that lead shot has been spec'd for many years as great filler for your stands - FRIENDS - THIS IS LEAD!! It is NOT good for humans. Use sand.

Years ago, I used a combination of BB's (anyone with an old Red-Rider BB gun in their closet) and fine sand to dampen the special speaker stands for my Infinity Infinitesimal speakers. This made the stands dead and quite heavy. You avoid any lead issues. BB's can be bought at most sporting goods store and probably available in bulk on the net.
Good luck.
Mike

Lead shot has also made rabbits and other poor defenseless, cuddly, furry animals DEAD!!! I could never subject myself to using lead shot, it would give me post traumatic stress syndrome........poor rabbits!!!!

If lead shot is outlawed, only outlaws will shoot rabbits. And they multiply like tribbles. Remember this, next time you have your ankles gnawed bloody by ravenous hares on your way to the garage.