There is an easier way to get the three X-02s rather than going through the entire game. After the game is completed, the "Free Mission" option will be unlocked. Select this option and choose a difficulty setting (normal for the gray X-02, hard for the black X-02, or expert for the silver X-02). Select any mission to play on that difficulty setting. If you get an "S" rank on all the missions, the X-02 becomes available. This allows you to skip all of the missions you got an "S" on when you went through the full game. For example, if you got an "S" on all but three missions, you only have to play those missions instead of the entire game.