i am fairly sure you can't.
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Yes the same way you get shiny Pokemon in the other Pokemon games is how you get shiny Pokemon in heartgold. There is a free shiny Pokemon in the lake of rage.
If you have shiny Entei, Raikou or Suicune from Diamond, Pearl, Patimum, Heartgold or Soulsilve, trade it to Black and put it in your party and go to Lostlorn Forest.
Luck. You have a 1 in 8,192 chance of your starter Pokemon to be Shiny.
I believe you can get a Shiny Stone in HeartGold in the Pokèathlon Prize Corner after you get 5000 Points.
To get any Shiny Pokemon, you need: LUCK