It is a website that lists all types of shooting supplies (powder, primers, ammo, etc) and the current availability. The site is updated hourly, and does not actually sell anything they just list the different vendors that have what you are looking for.
It is real popular due to the .223 craze, showing tons of what is actually available not just what is advertised but "not in stock".
I checked for your primers, and saw some listed for $36.99/1000 at Butch's Reloading Supplies. There might have been others, but at least they are available at Butch's.