Sorry you have not received a reply in a whole week. I get on here now and then and saw your post.
I have read many responses to this question over the years. The collective wisdom seems to say that there are only 2 or 3 manufacturers of the sheet metal for these trucks.
Original pieces will fit the best so if you can find some decent used pieces, that would be best.
I have purchased from Top Banana. They seem to be a shoestring operation that just drop ships. The parts were of decent quality.
I also buy from Truck and Car Shop. They have retail stores in CA and NC.
I have not tried FixMyRust.com but they have good prices and I think shipping is free.