We couldn't find it when we did the Royal Sport.  Convertible pieces are hard to make anyone give up.  My recommendation is to see how much of it he can make of the piece on his own or with some good friends.  In our case, the Camaro just needed the 6 inch section that went under the pinch weld so I got some cardboard.  The other brace on the other side of the car had the shape still so I copied it, then made it backward, a little welding, a little grinding, the awesome shrinker, stretcher from Eastwood, and in a period of about 2 hours I had it made.  If your buddy needs the whole piece well then I'd say BEST WISHES my friend.
Good Luck!

I heard recently that those inner supports are now being reproduced and sold... it seems that the Dynacorn people would make them in the past but were not selling them separately, only as installed in one of their bodies.