Like Mike Brooks, I use old coins. They are 90/10, and I buy them from a local coin dealer/pawnshop. He only charges a 3% premium over spot. I then pound them and anneal and pound and anneal and pound until they are close to the size I want. I keep telling myself I am going to make a roller mill to thin them as well as silver wire for wire work, but so far, that hasn't happened.
Matt