I finally got around to calling my friend who manages a large commercial tire shop, including a retread operation. He didn't even know that WW are made from lead anymore until he checked in the shop. One of his techs advised me that they have too much zinc in them, and would be bad for casting bullets - ? OK, I said, just save them for me and let me know when you have some accumulated.
Another friend who manages a commercial fleet of 100+ trucks is asking his tire supplier for lead on my behalf. So I might have free WW coming before too long - I hope, I hope...