I was bored, so....
Aircraft manufacturer representation in AH, followed by significant manufacturers not yet represented in AH. I have bolded the unrepresented manufacturers that I think had products that would fill significant holes in the planeset and/or were simply very significant players in the aircraft industry during WWII and listed some of their types I, or others, would like to see. This isn't to say that companies already represented in AH don't have useful things that could be added such as the Ilyushin Il-4 medium bomber or the Nakajima B6N torpedo bomber. The format I used shows aircraft by the manufacturer in AH, followed by the number of airframes in parentheses. For example, North American has four aircraft, the B-25C, B-25H, P-51B and P-51D making up two airframes, the B-25 and P-51.
Messerschmitt: 10 (4)
Supermarine: 7 (1)
Focke-Wulf: 5 (1)
Hawker: 5 (3)
Mitsubishi: 5 (3)
Republic: 5 (1)
Vought: 5 (1)
Douglas: 4 (3)
Grumman: 4 (3)
North American: 4 (2)
Lockheed: 3 (1)
Bell: 2 (1)
Boeing: 2 (2)
Curtis: 2 (1)
de Haviland: 2 (1)
Junkers: 2 (2)
Lavochkin: 2 (1)
Macchi: 2 (1)
Nakajima: 2 (2)
Yakolev: 2 (1)
Aichi: 1
Arado: 1
Avro: 1
Brewster: 1
Consolidated: 1
Kawanishi: 1
Kawasaki: 1
Ilyushin: 1
Martin: 1
Polikarpov: 1
Armstrong Whitworth: 0
Bloch: 0
Bristol: 0 Beaufighter, Beaufort, Blenheim
Cant: 0
Caproni: 0
Dewoitine: 0
Dornier: 0 Do17, Do217
Fairey: 0
Farman: 0
Fiat: 0
Fokker: 0
Gloster: 0
Handley Page: 0
Heinkel: 0 He111, He177, He219
Henschel: 0
Mikoyan-Gurevich: 0
Morane-Saulnier: 0
Northrop: 0
Petlyakov: 0 Pe-2
Potez: 0
PZL: 0
Reggiane: 0
Savoia-Marchetti: 0 S.M.79-II
SNCASE: 0
Short: 0
Tupolev: 0 SB-2, Tu-2
Vickers: 0 Wellington
Westland: 0
Yokosuka: 0 D4Y Susei "Judy", P1Y Ginga "Frances"