It’s a cage part, not sure of the specific part other than a bird food dish clamp, but you should be able to buy them at pet stores.
I went on line several auction sights and amazon, played with the words pet cage wall mount, bird cage wall mount, cage dish clamps, cage bar mount etc. you will find several things that are very close.
I found several dog dish mounts that were around $3.00 both painted and Steele will mount whatever between the bars so it doesn’t move, you would need a mount on the litter box, or drill and grommet a couple holes in the box so they cannot tip or move it around, nor can they chew the holes larger. The mate to what you have is something made of plastic or rawlite, a fiberglass plastic mix that rodents love to chew. Metal would be better, painted or coated even better, more resistant to corrosion.