Minus is a Pokémon from the *Pokémon Ruby and Sapphire* games, and it is not available in *Pokémon Colosseum*. *Pokémon Colosseum* uses Pokémon from the first three generations (Gen 1-3), and Minus is a Gen 3 Pokémon.
The only way to get Minus in a Pokémon game is to obtain it via trading from a game where it can be found (Gen 3 or later).