I just bent up my own out of .063. Installed with four #8 screws and nutplates.
If you don’t have a sheet metal brake, and know how to use it for the required bend radius, sandwich the sheet between a couple blocks of wood and hammer away.
Super easy part to make if you can’t find a vendor still making them.
 
Steinair

I have the Steinair bracket, high quality, milled construction, nice and stiff.
Bill Brooks
Ottawa, Canada