To be honest the most crab-laden rock I ever got (3 years on, I'm still convinced there are a solid half-dozen of the little buggers in there, I keep finding their discarded molts) came from a well-reputed store in BC.
Oh yes, mantis tanks. I forgot to list those.
I'd offer him to my eel but the eel already leaves alone the emerald crabs in the tank with him..