Yup. I agree with Norseman.
There ARE still some companies that get a decent supply of lead / antimony wheel weights, but they are mostly from semi truck / trailer weights.
There are still some good mom & pops style (non-chain) tire shops - focus there. They won't just give them to you or sell them too you. You have to earn their trust first. This is usually accomplished by purchasing several sets of tires from them over time and building a trust relationship.
I brought tires from my former employer to their shop regularly, got to know them on a first name basis, and brought them ~$5000 / year on average for business. Then brought them my personal vehicle tires too (~$500/yr).
After doing that for ~3 years I asked them about lead, told them what I planned to do with it... One of them was a Cap & Ball shooter that sometimes hunted muzzle loader. I bought a couple moulds to cast pure lead for his pistol and alloy for his rifle, and away we went.
I made about ~1000 balls / bullets for each of his guns, and since then he'd sell me a FULL 5 gallon bucket for ~$20 each. Since they needed some "proof" their lead was being recycled I whipped up a small batch of simple business cards... They would then do a cash sale invoice, and staple a copy of my business cards to each receipt.
I stacked up about ~700-800 lbs of lead ingots ready to go, and I moved out of state. As far as I know that company still does a lot of semi/truck tires and still gets a bit of lead in their business. They used to sort their steel & tin weights from their lead/antimony weights in two different buckets - making my purchase much easier.
Won't say the name of the company though. Anybody wants their lead they have to gain their trust just like other people. It's like was mentioned above - scrounge scrounge scrounge. Gotta find your own sources. I have three new sources up here in North Dakota, but I've cut back my purchases of lead because I've already got so much.
These days it's not much worth my time to cast my own - I can just buy Missouri Bullet Co ammo that's already powder coated and runs great.