Hi Zupe,
For an allied monoplane look at the Morane-Salnier Type N. Probably one of the coolest looking WW1 fighters. It didn't have a symchronized machine gun with metal reflectors to bounce bullets off the propeller. That's okay though as the Eindecker was fairly primative as well (didn't even have ailerons) yet it is in the game. This is probablour best bet for a single wing counterpart to the E3.