it might not be that rare, my LFS told me that it is a coral that can not be collected anymore because it is from Florida or the Caribbean. Perhaps there are pacific areas of blue coral. But, I guess the LFS is assured that this coral was from the Flordia/caribbean waters before the ban. They have never sold or fragged any of it. I have become great friends with the owner and they treat me right, so we fragged two small pieces and I got to keep one.
I also have a good size colony of Bariarium, which is another florida/carribean coral that can not be collected.