bigfootlarry, I believe 70sElvis has been looking since December. Unfortunately with that bracket being a one year only part, I don't look for those to be done by the repo people any time soon. The reproduction people are treating us better, but we are still last in line as far as they are concerned. D3ZZ-17787-A (right rear) and D3ZZ-17788-A (left rear) were discontinued by Ford in 1995. I'm really surprised they carried those parts until then. We have two Forum member/Venders that may be able to help you with a used bracket. Don (Ohio Mustang Supply) and Mike at Motorcity Mustang. They both have parts cars and are good at finding non existent parts. If not, maybe one of our Forum members may have a 73 they are parting out.
The only place I found a listing for the right rear is one I'm not familiar with. Don't really know how accurate their on line inventory is but might be worth calling.
http://www.rearcounter.com/D3ZZ-17787-parts1657291.html
For some reason when they listed the part they left the suffix "A" off. But the official Ford Part # is D3ZZ-17787-A. If you click on view profile, you will see contact phone numbers, address, and website.
Good luck with your search!