That looks like a part that you could home brew from a crank washer, with a hacksaw, a file, and a lot of patience. The tricky part would be the bent lip...crank washers are hardened and don't like to bend. Maybe the nuts and bolts aisle at home depot for a washer like a crank washer, only more malleable. A fabrication place could make it for you, but they'd charge a lot, so you'd have to buy 50 or 100 to make that worth your while.

Looking through my meager catalogs I see the same approach was used later, after they dropped the "C" from Record. Except that the end piece is cast and becomes the end of the pivot spring box. That would be a harder piece to get, I think. Kind of like that little stupid square piece with the teeth on one end that serves the same purpose on later Campy Derailleurs, and is just as often lost (I have two that are only good for parts because this little crappy piece is gone.)