I can't answer until you tell me exactly which legendary you want.
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The white legendary Pokémon is Reshiram, while the black legendary Pokémon is Zekrom. You can get Zekrom in the White version while you can get Reshiram in the Black Version.
Axew, Fraxure, Haxorus Druddigon
You have to either trade someone who has White version, or use codes to make one. Solosis is a White Version exclusive and cannot be obtained legally in Black version.
I am not sure because i caught him the first try, but probably not so save before him and stick up.
volcarona may not be considered to be a legendary as it does infact evolve from a Pokemon called larvesta, but the Pokemon volcarona is considered to be a legendary Pokemon.