You guys would cry if you came down to Florida to do some junkyarding. I see all of that stuff in rust-free condition all of the time, and cheap too. I think I pay $50 a door for any door I can find, and I see lots of rust free 80's GM products all of the time. Most go to the crusher fairly intact. There is no guarantee that any one yard will have the part you need, but between the 5 or 6 U Pull it yards I use, you can usually find whatever sheet metal you would need. In fact, I just saw a T-Top 81-88 Monte the other day and a Monte SS as well. Between the 3 yards I visited this week, there were about 10 78-87 El Caminos. Heck, if I knew how to ship the stuff, I would probably try to set something up so that I could sell it and make a little money!
As for where to find this stuff, you may wish to try thumbing through Hemmings to see if there is a junkyard that will ship.