The last lead smelter in the US shut down a long time ago, and really hadn't been a major factor in the lead supply even when running. Yes, its a bit sad to lose the "in country" ability, but we weren't doing much smelting of lead ore for some time before.
Much of the commercial lead supply has been coming from recycled lead for some time, along with purchase of "new" lead and recycled lead from other countries.
Wheel weights, bearing and babbit metal and some others can be used for many shooting applications, as it (for alloy content) and Lyman has extensive information available in the manual and books about alloying such sources for specific applications.
About every alloy will work as .45acp slugs, as long as its hard enough not to stick on the feed ramp, and there are many ways of doing that. Very hard slugs will also be fine, the low pressure and velocity of the ACP round makes it very versatile in that regard.