Rebuilding Window Screens -- Need Help on Corners

Trying to rebuild some mitered window screens. The plastic inserts that hold the frames together are all breaking (plastic junk). I can't identify the manufacturer and whoever installed them has been lost to time. The dimension of the inserts is 3/16 x 3/8 on six of the eight inserted legs. On the remaining two, there's an irregularity (which hopefully reads on the pictures) in order to accommodate a channel for some fuzzy bits(?). This last "leg" measures 1/8 thick for 1/4 on the outside edge and then goes back to 3/16 for the remainder.

It's driving me nuts trying to find replacements. Would love to do it in metal, but at this point I'd take anything. Many thanks.