Huh... looks like I could get you a Quiet 31/3/29/31/31/0 Kyogre fairly easily... IMO the Ruby/Sapphire weather legends are best with a speed reducing nature because they come at level 45. For using it in the VGC someone could use one of them at level 49 to be always be slower than the lv 50 ones from HG/SS, which ensures that you get your weather. That is the only unique thing that those legends offer from 3rd gen that is competitively viable.
I have to finish my current project though, which will take uh... maybe a week? Idk. The Kyogre shouldn't even take half a day though. That is if I can find warp codes for JP Sapphire.
Edit: My current project is a couple flawless Timid pokemon but the OT will be mine. In JP Emerald.