There is currently only one main way to get donuts which is the experience tournament. The tournament is not completely in the players control as they are competing against other players.
I suggest a new way to earn donuts called that would be a week long mission:
Tour of Duty:
level 1: 40 dual wins, 10 league wins, 15 training units used, 15 missions completed =5 donuts
level 2, 60 dual wins, 15 league wins, 25 training units used, 30 missions completed =10 donuts
level 3, 80 dual wins, 20 league wins, 35 training units used, 45 missions completed =15 donuts
Up to 40 donuts a week. Whatever numbers make sense. Have it be completely in the players control. Players should have a way to earn enough to activate all 4 boosters a week.