You won't find many Vietnam war games because its not an easy subject. It was mostly political and the battles that did occur weren't clear cut and didn't have specific conditions that would give one side a victory.
I mean, in WW2 you could have "Take out the artillery pieces so we can claim the beach". What could you have for Vietnam? "take out the huge underground network of secret bunkers the 'cong use whilst simultaneously killing the entire population of north Vietnam whom all will fight to the death to defend their beliefs" ? Napalm will only take you so far. Also, Vietnam wasn't America's best war, they kinda lost before it even began.
