I was recently running a 20mm boxer game at my club. Three players between them ran the legations while I ran all the boxer mobs.
I wanted to simulate the legations thinking about their ammunition or running out of it so I came up with the following idea. I used poker chips and each legation was given 3 red poker chips (fire chips). Each time the legation wanted to fire they handed in one of their fire chips which were placed into a bag. Inside the bag at the start of the game was a number of black chips equal to the green chips on the table.
At the start of each turn each legation returned their black chips into the bag and drew back up to 3 chips again. So if they no fire chips they would draw 3 if they already had two fire chips they could only draw 1 chip.
The system worked well with legations running out of ammunition and unable to fire, or holding fire when they only red chip left to save for emergencies.
Another alternative to make it even harder for the legations would be that each legation can only draw 1 chip per turn. I may try this another time.
The rules I used were my LOTR Strategy Battle Game variant found at the LOTR Variant yahoo group.