You can find it on Cheyenne Brass on the internet. I ordered a 1000 cases recently. They were very dirty and had been fired from a machine gun, so a lot of prep work is required, but for $160 (shipped) per thousand, they weren't too bad. Cheyenne Brass guarantees 95% usability, so out of a thousand you may have 50 casings that are other calibers, blanks, or too beat up to use. They clearly state this on their web site. There are other web sites that sell it, but most are more expensive and provide brass that is partially or fully prepped.
Jasper