Hi Marienwagen,
I also build in 1:72 and have been compiling a list of kits that have been produced over the years. This is by no means a complete list, but all those included have been seen for sale somewhere on-line (e-bay, or a seller's on-line store) over the past three years.
Here are the prototypes on that list:
AD Scout (EXPO Vac-Form)
Adamoli-Cattani (Choroszy resin)
AGO C.III (Merlin injection)
Albatros D.IV (Merlin injection
Albatros D.XI (Veeday injection, Choroszy resin, Formaplane Vac)
Albatros Dr.I (ELF injection, Choroszy & Classic Plane resin)
Albatros Dr.II (Choroszy resin)
Austin Osprey (RVHP resin)
Aviatik (Berg) 30.40 (Merlin injection)
Aviatik Dr.I (RVHP & Luedemann resin)
Blackburn Blackburd (Karaya resin)
Blackburn GP Seaplane (Contrail vac)
Caproni Ca.20 (Choroszy resin)
DFW T.28 "Floh" (ELF injection, Classic Plane & Wings 72 vac)
Dornier D.I (Meikraft injection, Choroszy & Luedemann resin)
Ducrot SLD (Choroszy resin)
Dufaux C.1 (Omega resin)
Fokker V.8 (Anigrand resin)
Junkers J.II (Merlin injection, Classic Plane resin)
Lloyd 40.50 Triplane (Meikraft injection)
Lloyd FJ.40 (Planet resin)
Mises-Aviatik G.I (Choroszy resin)
Nieuport Triplane (RVHP & Roseplane resin)
Pfalz Dr.I (although it did see limited production) (Merlin injection, Czechmaster resin)
Pomilio Gamma (Ardpol resin)
RAF SE2a (Aeroclub injection)
Roland D.XVI (Merlin injection)
Seishiki 2 (Choroszy resin)
Sopwith Swallow (RVHP resin)
Vickers FB26 (Scaleplanes vac)
Wight Quadraplane (RVHP resin)
Sorry I can't help with a full list of prototypes, but this should keep you busy for a while!
Ian