for these parts in steel, believe the only manufacturer / distributor is GoodMark. on GoodMark's website, steel hood and decklid noted made by Keystone for GoodMark. the buick vendors and other internet retailers are reboxing the GoodMark product as their own or drop ship the item from GoodMark / Keystone distribution centers depending upon destination.
you can buy direct from GoodMark but suggest calling sales dept for best pricing rather than using buy thru website. sometimes buy direct has best pricing, sometimes not.
HighwayStars sells these GoodMark items, but currently not in stock.
Partsplace shows them. have to call as they do not make it clear what you are buying as partsplace uses their own internal part #'s.
and many, many more resellers. a lot of searching for who has what available. pricing seems to vary a bunch.
In northwest NJ, i found a listing for 3 NOS GM turbo hoods for $1500 each. but I think you're on the gulf coast so it's a long drive to get them.