If your up for a big DIY task, you can contact the manufacturer and see if a replacement frame is available. If the tank is still in production, is should be, although manufacturers sometimes don't like to admit it.
You have to carefully remove the old frame. It'd siliconed on, so this often means cutting the frame in places to remove it. Then you remove all the old silicone and install the replacement frame.
I'm not too big a fan of trying to repair a frame or install a brace. It's really hard to get this just right.
As for replacing the tank. This can be done too, It's somewhat expensive, but you know you have it fixed then.