PlayStation Move Heroes

These enemies are pretty common. You will most likely get it when replaying the challenges for gold medals and collectibles. If not, start a challenge like Show No Merci in Downtown, Paris. In Wave 3, the game will spawn a lot of Boars at you, one at a time. Don't shoot the crystals, only the Boars and Pinbots so the rocket won't fill and yous should get many Boar kills before the challenge ends. Then just repeat.