Josef- Very rare. Took me 4-5 years to find them all. Mostly from haunting abebooks.com. On the Vintage Warbirds series, the latest I have is No 10, Nieuport Aircraft of World War One by J.M. Bruce. The only 3 purely on aircraft besides the one you have are on Sopwith Fighters, Fokker Fighters, and the one above. Other 6 in the series cover the RFC, German Army Air Service, RAF Between the Wars, Air War Over Britain, German Aces, and WW-1 in the Air. Bargains at their original $8.95 or so (vol 8) and still worth having.