ORIGINAL: tcrowson
Visit your local tire shop and see if you can talk them out of a bunch of used wheelweights. Then melt them down skim off the steel clips and cast them into appropriately sized and shaped weights.
Tas
This is what I do too. anyplace that does tire work from a big tire shop to a local gas station will always have a bucket full of those lead weights that they need to dispose of regularly. They are always happy to let you take a few handfulls.