Many pistols fit, very well, in a glock 17 or glock 19 holster. You would have to try your firearm, on these different holsters.
Find a very popular pistol, (like Beretta 92, or 1911) that is the general size of your pistol, and try them. A lot of holsters fit,
they just don't have "Rex Zero", or "FN 509" on the package.