To the best of my knowledge, nothing quite like that is available ready-made.
As far as inexpensive adjustable rings, the only thing I can think of is the ũ - Ŭ birthstone rings sold at state fairs. But the factory that makes the ring, is also putting in the stone, having it plated, and probably also putting 3 dozen in a ring tray. They aren't making any gluable or solderable items for jewelry crafters.
Then there are ring blanks for stone-setting. Most of these are with prongs, but some are with bezels. Some are for inlaying. But virtually none are adjustable. And most are precious metals, or at least sterling silver.
Perhaps you can figure out a way to make an adjustable ring out of wire, and do a little spiral on the top to glue or solder your items onto?
Then you can use any wire material you want ... Sterling, copper, niobium....
And (with a little practice) they would look a lot nicer than a mass-produced plated adjustable ring blank.
Try some Google searches for "adjustable wire ring" or variations, and see if you find anything inspiring. We also sell some good wire-working books to help you hone your wire-working skills.
--Polly