Your best bet would be to ask this in the helosim/flightsim forum. But as far as I can tell, there are two main games out there: First Eagles, and Over Flanders Field. Over Flanders Field is actually a mod for Flight Combat Simulator 3, and I think they're charging for it now.
All I can do is point you to those two games, as I've not played either of them. I think Mikhayl is a fan of First Eagles, so you might want to ask him. Good luck.
