This is quite a niche design, but if you happen to have an old Simpla-Lux cabinet that uses this type of shelf support, it could come in handy. Simpla-Lux was a Dutch furniture manufacturer from Uden, active in the 1960s and 70s, specializing in self-assembly modular furniture.

If you have a broken shelf support, you can replace it with a printed version of this design. In the first two photos, the original is shown on top and a print of this model below.