I use anything from 0.8mm to 2mm wire. A few years ago, I went on a hunt for a jig. I came up empty handed. So I got better at doing them by hand. Secret is in using the more malleable 304 S/S wire. Also, instead of using round nose pliers for forming the ring (I found that mine were not strong enough) I rather use circlip pliers which happen to have a good size round jaw. I did make a steel plate with holes drilled to accept steel dowels to help with the bend, but I found the circlip pliers to be faster and less cumbersome.
But if you're really set on a commercial bending jig, it wouldn't be too difficult to copy one.