If it was a British service revolver, it was probably .38-200, a British cartridge. If it is British, it should have british proof marks. I don't know where to find that caliber ammo. My understanding is that it is slightly wider and shorter than .38 special. I imagine some re-loader sites (perhaps here) can tell you where to find components or how to make brass.
If it is .38-200, it can be bored to fire the .38 Special. Most of the pistols returned to the US after WWII were re-bored and the barrels cut shorter.
My father has one that is nickeled .38 special, snub nose, with faux stag grips he bought while in the USMC between '57-'61. That was the configuration one distributor used to modify the returning victory pistols. They were sold cheaply to service members at the time.