Where do you get the regis in Pokemon Emerald?

Let me tell you where you can find all the Regis in Pokemon Emerald.

Regirock: You can find Regirock in the Desert Ruins; I dunno where exactly it is.

Regice: You can find Regice in Island Cave, which is in Route 105.

Registeel: You can find Registeel in the Ancient Tomb, which is in Route 120.

Hope I helped :)