Anti-vibration balls for hifi racks

I use a pro kitchen stainless steel table with six inch rubber wheels. It's mass is all I need. Plus I can move it for dusting. 

Silica (quartz) sand, as used in sandblasting, is what used to be recommended.

The only drawback is that the dust coming off of it is unhealthy - so fill items outside and wear a mask.

Once contained in a rack or stand it is no longer a health hazard.

If stored inside a lumber yard building it should already be dry (avoid sand stored outside on pallets).

Lead shot is difficult to dispose of properly, fortunately my auto mechanic accepted it for recycling.

DeKay

@incorrigable your idea may work the best for me!

The Star Sound people used to sell something they called Micro Bearing Conductive Steel.  Star Sound used it to damp their Sistrum Stands and their cables, and they sold it in plastic jugs for damping audio racks. I used it in DIY cables and still have a small jug of it.  It is no longer sold but it probably the same as, or very similar to, the steel shot for blasting discussed by @jsd52756. Maybe like this (link).

Lead isn't a hazard issue just pour melted wax into cavity to seal in the lead or whatever ...