Looks like part number FC424KL and FC424KR for 70-81 in Ames Performance would fit the bill. Look to be under $60 but the catalog on my PC is a little dated.
**I'm assuming you need the typical repair section which goes from the rear opening on the front fender to where it meets the outer rocker which is what the above part will do. If I'm wrong post a pic of what you need and I'm sure someone will chime in.
I'd imagine Classic Industries, The Paddock, NPD, etc will have these as well.