Well you could typ in a code to get him , or you should get the minikits (the last ones).
If you would rather put in a cheat code to unlock Darth Maul, pause the game and select Extras, then Enter Code. Enter one of the following codes to unlock the different Darth Maul characters that are avaialble:
Darth Maul – QH68AK
Darth Maul (Classic) – QH68AK