The best options for getting stone crabs are:

1) find an all-u-can-eat special (during season). Expensive, but worth it if you're hungry and love stone crab. The drawback - most AYCE specials are medium claws or smaller, so more work

2) find a local fish market that's carrying them - or even Whole Foods is cheaper than most restaurants. Take them home, wrap the uncracked claws in a towel, and gentle tap away with a good size hammer until the shell cracks and you can remove it

3) Avoid overpriced tourist traps like Joe's - you'll pay more than if you bought your own and enjoyed them at home, and you'll lose the opportunity to mix-match sizes or select specific claws

If you eat them at home, be careful with the shells - the fragments can be as sharp as cut glass and it's very easy to cut yourself badly trying to remove the pieces of they're not loose