Presumably you are referring to the big schools of Scalloped Hammerheads.
In my opinion, the best destinations for schooling Scalloped Hammerheads are in the Eastern Pacific. To Cocos (Costa Rica) and Revillagigedos (aka, Socorros, in Mexico mentioned above, I would add Malpelo (Colombia) and Galapagos (Ecuador).
These destinations are for all intents and purposes, liveaboard, except that Galapagos can be done land-based. But the Galapagos dive sites where you will see the most hammerheads, namely Darwin and Wolf, are strictly liveaboard.
This is not to say that they cannot be seen elsewhere, but the above are the places where they can be seen most consistently and in the largest numbers. Other destinations where they have been seen include San Salvador in the Bahamas, Tobago, Red Sea, Maldives, Taiwan, Layang Layang and Sipadan in Malaysia, Fiji, and Hawaii and both in el Bajo and Las Animas in the Sea of Cortes in Mexico.
Rangiroa in French Polynesia is better known for Great Hammerheads, not for schooling Scalloped Hammerheads.