Pokemon XD: Gale of Darkness Cheats

To acquire Shadow Dragonite, collect twenty Shadow Pokemon and ten regular Pokemon. Then, go see the leader of one of the gangs. Battle that leader and you will receive the Shadow Dragonite in return. (unverified)

Pokemon XD: Gale of Darkness Hint: Recapture Missed Shadow Pokemon
If you didn't manage to snag any shadow pokemon that you wanted, then keep fighting that Mirror B. guy until you catch it.

Pokemon XD: Gale of Darkness Hint: Sure Fire 1 HP Attack
All you need is a pokemon with the False Swipe attack. The Zangoose that you get from Zook has it by default. A pokemon with this move can almost always leave any opposing pokemon of lower level with 1 hit point, making it an easy target for pokeballs.