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.

Update: I bought some rings. They're okay. It's pretty hard to play with them and keep them from snapping to surfaces, and their sensitivity is pretty low - to get them close enough to stuff that you can feel them pulling is to get them about half an inch from the point where they'll hit the thing they're grabbing. My coating hasn't come off yet but I've only had them for a couple hours. They can make my computer go to sleep, which I already knew was a magnets thing because I wear magnetically clasped watches. I don't feel like I have an interesting new sense, but I have an interesting if alas delicate fidget toy, and my roommates have played with them too. Would not buy again, do not plan to go through the hassle of figuring out how to return.