Wheel weights are really not pure lead - they contain tin (and maybe antimony?) to make them harder.

You can try Midway in Columbia. They have a number of different lead formulations (Lead+tin+antimony) and I think they may even have fairly pure lead.

You can also tru Rogers in Liberty. They have lead ingots that I have used and they are pretty good.

The other alternative is to melt the weights as CN suggests. After skimming off the slag you can then pour your own ingots using an ingot mold.

Pete