Blue orbs are found during the races. There are several during the course of the game. After you unlock one, you can replay one of the races online or in local co-op and keep collecting orbs and replaying the level. Just do not exit the game completely and you will unlock this when you get to 300 orbs.
Also, you can start a single player race level and collect orbs. After you get right before the end, pause the game, and select restart level. Do this until the achievement unlocks.