Is there any legitimate way to acquire a Light Ball in Pokémon Black, White, Black 2 or White 2?
Wild Pikachu can be found carrying a Light Ball, but no Pikachu are encountered in Pokémon Black/White or Black/White 2. Pikachu can be transferred over from an earlier game (e.g. Pokémon Platinum), but items cannot. According to Bulbapedia, the Light Ball doesn't appear on any Dream World route or in the game Pokémon Dream Radar, and the Treasure Hunter on Route 13 doesn't give out Light Ball.
Is the Light Ball event-only in Gen V, or is there another way to find it without cheating?