sand versus shot in speaker stands

I've never dealt with commercial stands. The set I made many years ago, before I was even aware of hi-end were filled with Sackrete.
Could you still use lead shot if at the same time you mixed in some expanding foam? That'd seal in the lead at the same time as providing additional damping.
Careful of the ratio, so you don't get a geyser of foam.

You could always look for a well drilling supply place and get colorado silica sand of a given size range. You can get aquarium size sand in a sack, and it will not hold moisture and clump.

Kitty litter works too.

You can get clean dry sand from most hardware stores in a day or two. Just ask for a bag of Playground sand. I think it was 70lb at least 50lb and very inexpensive

Find a store near you that sells sand blasting shot. Make sure that is the silica sand type. It is dry and will not clump. I bought a 50# bag at a local tractor supply store for $8. It is more than heavy enough and does a good job dampening resonance.