Baseball Stars Color is a baseball game for the Neo-Geo Pocket Color.
Baseball Stars Color is a commonly available game for the Neo-Geo Pocket Color. It shouldn't be too difficult to find this game for purchase. In good condition, the game is worth about $10.00.
To unlock the hidden teams and players, you have to defeat all of the other teams in Single Player Mode. Because of this, the game must be played through a few times to unlock all four teams/special players.