Finding chrome or trim parts is a real task. I have a 77 SS and it's been a challenge. I found several parts here: http://www.trimparts.com/
Hope this helps you out... I'm still looking for fender well trim if you see any, please let me know!
Have you tried The El Camino Store? Some of the places I have seen or noticed had the bed chrome have an exchange program. They charge a "Core Charge" if you don't supply them with the old stuff. 73 ~77 parts are difficult to locate and most parts are used. So to keep up the supply some places require that you trade in the old bent up stuff so it can be repaired.
I had a company in CA. offer to redo all the Chrome on my 76 Classic for $1,800.00. They stated it would be triple chrome plated and show quality. I didn't go that route and it was a long time ago so I don't remember who it was. But you can find these places.