All and all, one needs to complete 22 Class C Missions. These missions are:
Missions 6 - 15
Missions 18 - 22
Missions 35 - 37
Missions 56 & 57
If you are attempting these missions post-game, the foes are generally rather easy to beat but the time needed to 5 star them is usually quite short, so you should remember that shrouds and pre-emptive strikes (where possible) will be your friends. Fortisol FTW!!!