You would need to have it traded from a B/W that has it. To get it for B/W:
>Held by Singing Pikachu, Pikachu Festival Pikachu, Pika Pika Carnival Pikachu, Japan Expo Pikachu, Pokémon Day Pikachu (Italian, German), Summer Carnival Pikachu, World Championships 2012 Pikachu (event)
These were all Events that passed; you need to trade if you didn't participate.
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