As far as I know the under bed part is not reproduced, but you can usually find used ones still.
Here are some photos of the one on my '65 c10:
09/25/2006 : 16 pics — under bed spare tire set up
07/30/2017 — under the bed spare tire holderI took out the plastic piece in the part that secures the wheel and had some nuts welded on each end of the correct thread. That plastic piece had a habit of breaking, which is why you don't see a lot of the trucks with it still on the truck.. that or some later model exhaust routing put the tire in the way.
Used Parts:
One of the best places to look for used parts is here on stovebolt.com:
Swap Meet area of Stovebolt.comLook under parts for sale or place an ad in Truck parts wanted.
More used chevy truck parts searching tips:
An article about searching for used pre-1973 Chevy/GMC Truck parts.Enjoy, good luck.
-Woog