a long time ago I fought Gettysburg (among others) as board games using 'Kriegspiel' rules. It was also one of the first computer games I ever played - released by Avalon on Atari 1020.
In both cases ammunition supply/resupply was handled by a calculation depending on distance from the next-up HQ and Line of Supply, rather than any physical objects on the field.
I think something similar should be considered here, this involves less micromanagement, or 'gaming' by deliberately going after units ammunition supply, which would strain the AI to cope with (IMO)
Cheers
Lucius