Well,
Let's look at the guns of that era that were in use at the time:
USA: 1911, Colt 1917, S&W 1917. 2 of these are still in production. The 1911 is under manufacture by at least 10 companies off the top of my head, and S&W brought back the 1917 as a performance shop model.
Britain: Webley MK VI in .455, great revolver, production stopped in 1918, hasn't been seen since WWII.
Russia: 1895 Nagant Revolver. Still in use by some railway and rural police forces in Russia.
Germany: 1908 Luger. Still made, but serious use stopped after WWII.
Italy: Some 10.5 MM Revolver, or something like that.
Austria-Hungary. The Rast...
Of all the WWI pistols, the 1911 is still the only one in production and has been considered the best design of all time.
Yeah, I want one, want one bad...