I dont think WWII pilots were issued revolvers in general, the only exception I can think of was the RAF that carried two versions (II and IV) of Webley Service Revolver 38. This was a critical shortage of handguns in the UK when the war began so when lend-lease started most had been issued the American Colt .45, or Browning HP.
So to answer your question, revolvers were relatively rare amongst aircrews, I dont think the RAF issued speed loaders so I would imagine any spare ammo was carried loose. Keep in mind the Senojekips is right, being shotdown in enemy territory usually meant death or capture. A Pistol wasnt going to get you far against an enemy carring rifles and submachine guns.