These events, like everything else, are unlocked though completing challenges and earning fame points. Keep earning points and complete as many media and sponsor challenges as you can and these events will unlock on completion of sponsor challenges. When you unlock a new event you will be prompted with a flier on the screen telling you where to go for your event. Keep up to date by using your phone, as you will be required to reach a certain number of points for each event to open.
These events can be a little tough to win, but make sure you beat the pro's score on every round to make sure you beat the event.