There are vendors online who will sell you silver core wire. I went to Homegrown Audio, which sells it in bulk or braid. I chose braid since doing so does the work for me. I went for a four-wire braid, two strands of which were in white teflon while the other two strands were in clear. It cost me $12/ft but for a little less than $50, I got four feet (more than enough to connect to my iPod). There's a $10 charge for shipping and a plug will cost you $5, but for $65, I got an awesome four-braid cable. All I had to do was solder and I was good to go.
Oh yeah... I forgot about that silver wire. I suggest the Cardas litz cable, you get two litz cables (google it) that are wound around each other and shielded. That, and your two channels are separate, so there isn't any crosstalk between the right and left channels. $2.10 for a foot, but you get two wires instead of one. It's not silver wire, but I think the construction of the wire is more important than the material.