As derangeddarling points out, there's a replica tie-in ring on Amazon*--but it's the silver ring (left side of the picture; bottom of picture). But that's the thing--it's a ring you see prominently before they get to Tia Dalma's. Which only makes it weirder that Tia is specifically shown with that ring on the official site. (They've added a token-collecting game--yes, a second one--since the last time I mentioned it; the ring was not there in the original version of the site.) To complicate the question of whether Jack took her necklace or not--people seem to be saying that he leaves it on the table and takes only the ring--Jack is shown wearing the necklace on the site. But you can also see a smaller version of the same green and silver ring (Tia's is so large because you're supposed to click on it) on the correct hand. BE MORE CONSISTENT WITH YOUR CLUES, PEOPLE!
* Wear Johnny Depp's ring! One of Johnny Depp's own rings, worn to the set one day, looked so perfect for the character of Jack Sparrow that it was quickly adopted as part of the flamboyant pirates costume.
"Hey, man, can we make replicas of your ring?"
"Uh... that's kind of creepy, actually."
"Excellent, we'll get right on it!"