Who sells lead shot pellets to fill an equip.stand

Finding a local gun or trap and skeet club might solve all your problems... if you have to get lead.

Bob at sound Anchor says other things will do just as well, be less of an issue obtaining and disposing of, while being both cheaper and safer. Cat litter or sugar sand do work. A few tubes of silicone & latex caulking being applied alternatively and left to set up before applying the next amount, could work too.

Does anyone know how to dispose of lead shot?

Krell1- For disposal I would look to a metal recycler, otherwise you are talking hazardous waste! One of the reasons to use steel or a substitute. Since the lead shot is 100% lead and the action levels are in the parts/billion range, you can see that even a v small amount of dust generated from pouring/handling can contaminate a large area, and one pellet ingested by a child or animal can cause acute poisoning.

I filled the hollow parts of my turntable table with vermiculite on the recommendation of the dealer. The table is completely dead sounding when tapped. It's readily available as a gardening supply

Lead shot was banned years ago for waterfowl hunting because it was being ingested by birds in the marshes. It's still allowed for upland hunting.
Because of the ban other non-toxic shot were introduced, the primary one being steel but there are others. If you want shot for your speaker stands seek out these other non-toxic materials. Any shotgun reloading supplier should have them. Because of weight and cost of shipping I would try to find a local source.
They come in different sizes, the higher the number the smaller (9, 8, 7 1/2, 6 etc.).
You should only use lead if you're into heavy metal 8^).