Celebi isn't available in Pokemon Black and White. You have to transfer it into Pokemon Black and White or trade for one.
Chat with our AI personalities
you can't
You cannot catch Celebi unless you are using cheat codes or waiting for Pokemon events.
In order to get Celebi on Pokémon Black without an event, you will need to trade for one or you will have to use a cheating device such as an Action Replay in order to get Celebi.
YOU CAN'T GET CELEBI IN DIAMOND WITOUT MIGRATING
In order to get a Zorua, you must first have a special celebi that was given out. Then you must transfer it to Pokemon Black/White using the Pokemon Relocator. Have celebi first in your team and head to one of the buildings in Castelia City. Zorua is disguised, but is next to a female character on the bottom floor.