White Wire Shelf Corner Support Bracket Replacement for ClosetMaid Shelf - Adjustable Ventilated Wire Closet Shelving Accessories Support Brackets for Wire Shelving Corner Support, 2 Pack

Interesting you needed to supply your own solution. Did you install the original shelves? When mine were installed in a configuration similar to yours, my installer seemed to utilize a small flat 5" by 3/4" white metal piece that seemed built for purpose. It has a bend in one end like a tab that slots between the spaces in the shelves and a curve at the other end that slots over the more solid piece a bit back from the front. ETA, looks like they're on Amazon https://www.amazon.com/Trdzi-White-Corner-Support-Brackets/dp/B0DG8TYZPG