You cant, you have to trade him from a Pokemon Diamond game.
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In Pokémon Pearl, you can only obtain Dialga by trading it from Diamond, Platinum, HeartGold or SoulSilver.
In Pokemon Diamond, Pearl, and Platinum, you cannot 'recatch' Dialga, but you can have multiple attempts if you save before battling Dialga. In Pokemon HeartGold and SoulSilver, when you do the Arceus event, you automatically obtain your choice of Dialga, Palkia, or Giratina.
no
The card key in Pokemon Heartgold and Soulsilver is located in the Goldenrod Underground.
The Quick claw is located in the National Park in Pokemon Heartgold and Soulsilver.