This trick gets you as many AT-AT or Tie fighter bodysuits as you could possibly want (no helmets).
I figure this should also work with the B-Wing suit, but I'm not a Rebel so I can't do the mission.
1. Get to the last mission from Thrawn (mission #6) in the Imperial Theme Park.
2. Fill up your entire backpack with items, and fill up your entire inventory except for one space (59/60 inventory, 50/50 backpack).
3. Complete the mission and talk to Thrawn for your reward. He will stick either an AT-AT suit or a Tie suit in your inventory (at random), and you will get a message saying you need to clear up space in your inventory to finish getting your reward.
4. Clear up exactly one more space in your inventory (59/60 again), and talk to Thrawn again. He will give you another bodysuit, and tell you to clear up your inventory space again.
5. Rinse and repeat.
The easiest way to get a full inventory of suits is to fill most of your inventory with resource stacks of 1. That way, when you need to make another space in your inventory, you just drag-and-drop one of the stacks of 1 onto another stack.