This is one of my favorite fish. I've had 4 over the past 20+ years, and every one I caught myself. The shallowest I found them using scuba was about 70 feet, but they like deeper. They are, in the wild, almost always full size. I've never seen a juvenile. I suspect they are found in even deeper water. Bringing up fish from deep water is always a problem, especially with mature fish. I've lost a few that way.
They are extremely hard to catch, tending to swim away in a straigh line, very fast, not stopping and usually not holing up is a crevice. I have not seen them for sale in local shops, and I'd be hesitant to buy anything I have not seen first. Air bubbles and bouyancy can be the kiss of death.
That said, they are a wonderful fish, delicately colored and lovely, eat blackworms ravenously, adjust to any meaty sea food I've tried, and have swimming habits that are unique. They have a lot of very attractive qualities.
I saw one last year in Dominica while snorkeling in 10 feet of water near a drop off. As soon it saw me it took off in a straight line into deeper water.