Ring bending pliers are sold at every tool dealer int the business -
I would offer up, though, that if you're doing a lot of work, what
you could use better is a ring bending MACHINE. I don't know of a
comparable, ready made device that's geared to bracelet size, though
- you just have to be careful not to curve the stock too much. A
ring bending machine (not cheap, but the best) mounts on a bench, and
has a short, stepped mandrel with a big handle attached. in the base
is a die, also stepped, which meets the mandrel. You put your stock
in it, pull handle-feed, pull, feed----voila', a nice, clean circle.
They are great, they are stout - indispensible, to me. If you see a
photo, you'll see better what I'm describing.