Terry,
Those are called corner nut plates. Specifically, those are "mini" corner nut plates. I have a bunch of these. They are very handy. They are part number MS21073-xx
Wicks carries them. Below is the link for #8 screw size.
http://www.wicksaircraft.com/catalog...070/index.html
So does Genuine Aircraft Hardware Company
http://www.gen-aircraft-hardware.com/default.asp
B&B Aircraft Supply also carries them.
http://exp-aircraft.com/vendors/page...-Supplies.html
I've found that when looking for that really hard to find aviation hardware, the place to go is M&M Aerospace Hardware. These folks have EVERYTHING!!
http://www.mmaero.com/cm/home.cfm
They sell mostly to FBOs, but will sell to individuals. You will need to set up an account with them.
Charlie Kuss