Pins, buttons, and keychains have always been a big part of our little fandom here. Pretty much every artist out there that sells at conventions has done one of the three. We;ve got another one up on Kickstarter from Squididdle, starring all four of the princesses in enamel form.
If you are interested in hopping on board, you can find them all over here, along with prices. It doesn't look like there are any stretch goals, so I'd expect a round 2 if these end up being successful!
As always with kickstarter projects, do your own due-diligence. Make sure you are comfortable with the creator.