With the onslaught of thin, Chinese, junk metal repair panels, I've gotten better at making my own. I use 18 gauge steel for everything unless it needs to be structural. (ie: a stiffener for mounting something) Then I'll use 14 gauge.
This isn't a Chevelle, I'm just throwing out the fact with minimal tools, (in this case a flat body hammer and a 2" round length of pipe) you can get some pretty decent results.
Here's a compound curve in a wheel well arch I did.
...and here's the trunk pan of a '61 Bel Air I'm doing.
Before:
And after:
Also, if a repair panel isn't even offered, ...I have it. These are floors I did to mate a '66 Ford truck to an '85 Bronco chassis while using all the factory mounts for the Bronco interior and center console.
A piece of 18 gauge sheet metal that comes in 4'X8' sheets costs me $40. I can typically do two cars worth of repair panels with that, at least. Yes, it takes more time, but time doesn't cost me anything out of pocket. It also doesn't matter if a repair panel is hard to find or not. With a little time, I have every repair panel I'll ever need leaning up against the wall of the shop.