I'm not sure if this is the correct section for this, but I saw this tank on craigslist ( http://newjersey.craigslist.org/for/2280398207.html ). Being that the back piece is broken, would that affect the integrity of the tank?
I wouldn't trust it with the broken support, but I know I've seen people who have replaced the framing on their tanks. Unfortunately I can't remember who or where they found them online, but a little searching should find one for you, also your LFS should be able to order one. Depending on what the frame will set you back it could definitly be worth picking up the tank.