You can capture it in the safari zone but it's kind of rare.
I don't have all info but some pokémon sites probably says how to make it happen.
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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.
You can't. You need to get Heatran from Pokemon Diamond, Pearl and Platinum and then trade to heartgold and soulsilver.
In HeartGold and SoulSilver, she does not battle you - which might be one of the reasons why she doesn't have a starter pokemon. Instead, she has a Marill.
The only way to get a gligar in pokemon soulsilver is to trade with pokemon heartgold.