You can't find richu in the game unless you have a cheat code of some sort. If you use a code to find a pikachu, you can use a thunderstone to evolve it. Go to supercheats.com, look under Pokemon Black cheats and you should find a panel that says "Pokemon Modifier". Enter it into a action replay (if you have one) and follow what the panel says in how to use the code during the game.
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Yes. You find zekrom in Pokemon white and the white Pokemon in Pokemon black.
Nowhere. you can find the Black city in pokemon black and White forest in pokemon white. YOu can't got to the white forest in pokemon black
Celebi isn't available in Pokemon Black and White. You have to transfer it into Pokemon Black and White or trade for one.
Trade from white and if you have white trade from black for tornadous
Eevee cannot be found in pokemon black or white, and must be traded to be obtained.