You gan get Kyogre in Saphire in the Cave of Origin Basement and in Emerald in the Marine Cave.
Finding him is easy, but catching him could be a chore and a half (if you get where im coming from here)
You're gonna need a Poke with some good SPD to wall him, or good Physical attack (like Blaziken, risky but worth a shot)
Make sure you bring all of the healers, ultra balls, and other stuff that you need. I also reccomend grabbing yourself a Tentacruel (Using toxic will help)
Heres my strategy for you.
Once you engage him, you will want tentacruel to poison him to get things started, then give him some punishment (for this example i'll use blaziken's double kick)
Once he's weak, start doing attemps to cap him (may not work perfectly for the first few trys but you'll get it in a while or two) then you should have him!
Paralys and sleep work if you can get the right movesets.
Kyogre's strong points are special attack and defense, and realatively low physical defense.
Hope this helped! Happy Gilmore! (capping....erm...sorry!)