It's not rare. Don't believe the LFS. It's just a wild colony, like the ones that came in dead above. They make those concrete bases, and tie them to a bamboo grid, and suspend that from the ocean floor in shallow water, with small pieces of coral attached, which they plucked from colonies on the reef.
In a short time they are the size you see in the pics and are ready for sale. They ship them in boxes of 18-25 to california, where your LFS orders from.
Harder to keep than corals that have been in synthetic water and artificial lighting for generations, but not impossible.
I have a few wild pieces in my tank right now doing ok.