I believe I got mine from wirecare.com, but I'd have to look to be sure. The size that I use most is 3/16 I think, I'll double check that for you as well. I'm still working off the 200' spool a bought a year ago but there's less left than I thought...
For IC's I think I've found my favorite in 24ga UPOCC in PVC. The last batch I got from Take5 had a thinner pvc jacket than some of the other stuff that I've gotten from them and worked really well. Not good for headphone cables though. For headphone cables I really want to try 28ga UPOCC in teflon, that'll probably be what ends up on my HF1s or 2s. If you want to try UPOCC let me know and I'll get you some with my discount.