Where can I find Kyogre and Groudon?

After you beat the E4, go to the Weather Institute, and talk to the man. He will say something, and the route they are located. To find Kyogre use Dive, and to find Groudon use Watterfall then go into the cave. And yes, you can still catch Rayquaza.

Yes, you have to beat the Pokemon league to catch them.
The good thing is that you can catch all three {Kyogre, Groudon, and Rayquaza.}

You can catch groudon and kyogre after you beat the Pokemon league
To catch them you have to go to the weather institute and talk to the scientist. He will tell you the location of kyogre and groudon.
Yes you can still catch rayquaza

After you beat the elite four go to the weather institute and the guys will say that there is some unsual weather happening on a certain route go to that route and you should be able to see a cave or a place to diva at then you can catch them,to catch rayquaza you need to go to the sky pillar at the top he should be there

First you beat the elite four ,then you go to the weather institute and talk to the guy on the top floor he will say something about a drought somewhere catch groudon with an ultra ball and after you catch groudon go back to the weather institute and talk to the same guy who gave you castform he will say something about a rainfall don't use your master ball on kyogre either save it for latios or latias hope this helps p.s you can catch rayquaza after the fight with kyogre and groudon .