http://www.flynbye.com
Owned and operated by thirdgen.org's own ebmiller88. He sells a rear drum to disc conversion and all kinds of front brake solutions.
Depending on your axle though, you might want to just keep it drums until you can find a better replacement. When you can pick up a 4th gen axle for $200 disc-to-disc with posi, spending $85 for the brackets plus new calipers, rotors, pads, and everything else (If you have a posi, it might be worth upgrading brakes, but if you have an open diff with drums, find a whole new axle.) gets really expensive really fast.