Drawer slide rear mounting bracket

I have searched all over and have struck out in finding drawer slide rear mounting brackets that even closely resemble the two attached photos. Can you help? The square opening that receives the drawer slide measures 5/8" by 5/8" square. The "T" slit at the top measures just under an inch across. The base is 1 1/2" square. My kitchen drawers have no stamp or identifier on them as to brand or anything so no traceability there. The home was built in 1989 so that dates the manufactur of all cabinets and drawers around 1989. I can't believe that I am having such a hard time finding a few of these rear brackets. There's gotta be a warehouse full of these somewhere.