Contact your area gun clubs. In my state, at least, they are rquired to have an environmental program, and that means they mine lead from the berms, indoor pistol ranges, etc. You can get tons of the stuff that way without grubbing in the sand berms and breathing god knows what. We had multiple fifty gallon drums full of lead last time we mined the indoor range.
But considering just how dangerous lead is, it may be better to just buy your minis, round ball, etc. More expensive, but safer.
Dane