How do you find regi ice regi steel and regi rock?

Before you find the three Regis, you need to unlock them in a Sealed Chamber off in the ocean currents west of Pacifidlog. You need the Pokemon Wailord and Relicanth and the moves Surf, Dive, and Dig.

Start in Pacifidlog and ride the currents west, but be sure to lay low against the southern rocks to hit the mark. After a while, you'll come to a dead spot in the current surrounded by rocks. There's a diving spot here, so hop into the dark patch of water. Make your way through the trench, and soon you will come to several dots on the wall. This is written in Braille code, but it says "GO UP HERE". Directly in front of the tablet, surface the water, and you will have entered the Sealed Chamber.
There will be several tablets that will help you decipher the key, but you don't really need it. Walk straight to the back to a tablet that reads "DIG HERE". Follow instructions, and use Dig in front of the inscription. A door will open up to the next room.
There will be seven tablets, each with inscription on them, but focus only on the tablet in the back of the room. It reads "FIRST COMES WAILORD, LAST COMES RELICANTH." Put Wailord in front of the party, and Relicanth in the back, then read the words again. The three doors will open in the distance, unlocking the three Regis.

HOW TO CATCH THEM:
Required (all 3): The moves Flash and Rock Smash

We'll start with Regirock. Located on Route 112 in the midst of the desert, Regirock will be inside the Desert Ruins. Inside will be a large room with Braille in the back. The Braille reads: "LEFT, LEFT, DOWN, DOWN. THEN USE ROCK SMASH." As it writes, take two steps to the left, two steps downward, and them use the move Rock Smash in that exact spot to open the door. Regirock is inside at Level 40. Have plenty of Ultra Balls.
Off the coast of Petalburg on Route 105, Regice sleeps in the Island Cave. Inside is the same basic thing: a large room with nothing but an inscription. It reads: "STAY CLOSE TO THE WALL. RUN AROUND ONE LAP." Make one complete lap around the room, staying close to the wall. If you made one lap around without missing a step, the door will open. Regice is inside at Level 40.
Last, but not least, Registeel. Hidden away on Route 120 inside the Ancient Tomb, Registeel is the hardest to capture (well, for me anyway, probably not for you). Inside is the usual: empty room and words. The words read: "THOSE WHO INHERIT OUR WILL, SHINE IN THE MIDDLE." Go to the middle of the room and use Flash to open the door. Registeel is inside at Level 40.

COLLECT ALL 3!!! =P