Z71 Rusted rear bumper

[Under the Palms]

We have a 2003 Z71 and the rear bumper has completely rusted out, this all happened since last winter. I originally took it to the dealership I bought it from, and they were going to replace the bumper under warrentee, due a a personal situation, I was unable to leave the truck for 4 days at the time. Now I'm ready to sell the truck and need to get the bumper replaced, in the mean time the dealership went out of business, and now I'm on my third dealership and everyone is giving me a hard time about fixing it. A friend has a twin of the truck, and her bumper rotted out also, the dealer she got it from fixed it over the summer no problem, when I call the warrentee guy won't even return my call.

Any ideas on how to get this taken care if? This is my third new GM vehicle in a row, I'm starting to have second thoughts about going GM again.

on another angle, anyone know a place I can get a cheap replacement bumper?

THanks,
Todd