You must have the 11th movie event Regigigas in you party. to find the 3 regis pokemon, just go to:
Regirock - Cave on route 228
Regice - Cave inside Mt.Coronet
Registeel - Cave inside Iron Island near the exit
just go to the cave and awake them by stepping on a pattern on the floor in that cave, and they will be at Lv30! hope this usefull...