Nobody sells them that I found...I tried Advance auto parts, Auto zone, Sears, Napa, and Snap-on. Ended up just buying a new tester with a bunch of adaptors (including the right one) off eBay for $60. I know they have them at Northern Tool, they were out of stock at the one here though, and werent expecting any for a couple weeks. They do have a website you can order through if theres no store by you. Would also check Harbor Freight.