I didn't want to be an advertisement so I didn't (mean to) link. (woops). Try ebay for magic rings, or magnetic rings, also aliexpress, also you can email the guy at supermagnetman and ask for other sizes. I would suggest going on the tight-side of sizes because they like to pull themselves off when they find metal to attract to.

I have been wearing a black epoxy coated and a silver one, and I do a hell of a lot with my hands, so I expected the coatings to come off. which happened. I figured this would happen, so FYI.