There was one in Council Bluffs,IA, The Western Front Dawn Patrol. I don't think they've had one since 2010 though. Dean Dingman was the organizer.
[email protected] or
[email protected] are the Email addresses I have for Dean, but they may not be current.
And near Eureka Springs, Arkansas there is
http://www.dawnpatrolsquadron.com/ It's in June. While not strictly WW1 it's an wonderful event.