After catching Kyogre, obtain a Groudon from a friend with Pokemon SoulSilver. You only need the Groudon temporarily. Talk to Professor Oak with both in your party, and Professor Oak will give you the Jade Orb to catch Raquayza.
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No you do not need to catch Kyogre. You can get a Hoenn starter from a guy named Steven in Kanto.
You cannot catch Kyogre native in Pokemon Diamond. You must import the mighty Kyogre from Emerald or Sapphire using Pal Park.
Groudon is unavailable in heartgold. You can only catch Kyogre. If you want groudon, you will have to trade from heartgold, or migrate from another game.
You can't. You must trade Kyogre over from Heartgold.
In heart gold after catching Kyogre you will have the Blue orb. Get someone to trade you a groudon only then you can get the jade orb and catch raquazza