The Shiny Suicune was a game stop event held before Pokemon black and whiter where releases. You had to get either suicune riakou or entei at the event of your Pokemon Pearl/diamond/platinum/soul silver/ or heart gold version, and then transfer them to your Pokemon black/white version.
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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.
You can find a Shiny Stone in route 6.
route 1
If you mean how to get shiny pokemon in Black and White, then it's all by chance. The odds to find a shiny are 1 in 1892. That's only 0.0122% of a chance. They are random to find. You can also use Action Replay to cheat yourself some shinies.
It is almost impossible...but you can still do it. When you first get your Charmander, Suicune is released into the game. But you have to beat the Elite 4 and do all of the after game. After you have done all of that, you can go and catch Suicune. Run around until you encounter it. If it is not a shiny, then you have to reset your game and do it all over. As I said, it is nearly impossible. But if you reset your game enough times, you will eventually encounter one. Suicune remains the same no matter how many times you encounter it. Also, keep in mind that you have a 1/8192 chance of finding a shiny Pokémon. It could take YEARS to find a shiny Suicune in Fire Red. Hope this helps :)