Fiv3, see if you can get used lead wheel weights from one of your local tire stores. I live in a small(ish) town and I drop off a five gallon bucket. When it's full, the manager calls me. That bucket lasts quite a while!
If you've got a metal recycler in town, check with them - they may give you a deal on scrap lead (probably the wheel weights that the tire shop wouldn't give you!)
It takes a little extra work to pick out the steel "hooks" that attach the weights to the wheel and you have to also pick out the zinc weights that also get tossed in, but if you get the stuff for free, that's a small price to pay.
EDIT:
C.Robertson, below, is right - wheel weights are too hard. I let my fingers run away from my brain...I cast wheel weight bullets for BP cartridge guns. I get soft lead from the recycler. My bad, and thanks for bringing it up. As soon as you try to load a wheel weight ball into your revolver, you'll see what he's talking about
