They are't that rare... I have no less than 10 colonies of the tube corals that came on my Florida Aquacultured rock, and that isnt including the 10 or so that didn't make it. It was covered with it. You just can't buy a colony of it, you have to get the rock with it attached. Tampabaysaltwater.com sells their deco rock thats covered in it. Out of the 140lbs of rock I got from them, only the base rock didnt have at least a golfball size colony of the "RARE" Atlantic coral.
Here is an old picture I have that I took the day the rock came in. For reference, the clam in the middle is the size of a baseball, and even it has a tiny colony growing on it.
