I am in the process of installing my new fiberglass door panels from 914 Rubber. It looks like my door panels were pieced together with parts from the bottom of the scrap pile. That's only the half of it. Heck the last person did not even remove the old vinyl before installing the new stuff. But I digress.

Looking for at least 4 of these mounting brackets if there is a source.

Click to view attachment

AA has this:
DOOR PANEL 5MM CAGE NUT; 914 1970-76
R99950731702 - Replacement/Accessory


Price: $3.50
Description
Cage nut used to secure the side box to the door panel. this part actually clips into a square hole in the door. two required per door. order the 5mm allen bolts while you are at it.

also have some other stuff:
http://www.autoatlanta.com/results.php

Description
Cage nut used to secure the side box to the door panel. this part actually clips into a square hole in the door.

.....they do clip to the door

I think they meant to say the cage nut clips to the black rectangular base attached to the back of the door panel. It's not the best description, but it seems to me it is the part he is looking for. These things fall off all the time and get lost.

Those nuts are a standard item and a good hardware store should have them.

If you have a Grainger account, I know they have them and so would your local Fastenal dealer. The "real" price is less than a buck a piece.