regi's

You must have Dive, Rock Smash, Wailord, and Relacanth. There is a deep sea spot in the tides next to Pacificlog Town. The place there holds a chamber with a crumbly-looking wall. You must have Relacanth in the first slot of your team and Wailord in the 6th (Or the other way around). Then use Roch Smash on the wall and it will crumble. Walk through the entrance and progress further, then you will realize a shaking. The 3 rock shrines throughout Hoenn are now open. Access them and follow the braille instructions to fight each Regi. I recommend you get a Braille Decoder from somewhere of the net so you can define the braille in all the temples.

There's a place underwater west of Pacifilog Town. Go inside and and break the wall to enter the chamber. A cutscene will happen and the three Pokemon can be found all over Hoenn.

To find the locations you need to decode the messages on the wall wirtten in braille. At the back of the book that comes with the back there is a decoder, but if you don't have that you can search the internet. You can also use a walkthrough guide to finding them. Last I remember the Regice is west of the entire Hoenn region in a caveon the sea.