You can order brass direct from Starline. http://www.starlinebrass.com/
MidwayUSA also sells Starline brass for a few dollars more per 500/1000, and you can order bullets at the same time to possibly save on shipping costs.
Lots of others, I'm sure. If anyone knows of a cheaper place for either, I'd appreciate it too. I'm going to order brass and bullets pretty soon.