Is it possible to replace a 2004 pontiac gtos rear bumper with a 2005-6 bumper? Where can i find one?

You can get one from the dealer, but you'd need to change to a dual exhaust setup like the newer ones. I'd also consider changing everything else over while you're at it. Those first 04 models were so dissapointing...they fixed it a bit in the following years though. Good luck!