Do you want paper or fabric? A good place to start is model ship accessories--preferably the larger scales. Since a flag waving on a tank would represent a good target or place for an enemy tank gunner to sight on, most were, like I said, draped over some horizontal surface so friendly fighter planes wouldn't mistake the tank for enemy and strafe them or drop bombs. I've seen the Nazi flag draped over Tigers for aerial recognition.

-Harq