Sean you will be able to find a holster for it depending on your personal taste. I have used this weapon before with a Navy supplied leather holster. I cannot remember the holster brand, but the military were not the only people using it. A little history for you to help in your search.
The Illinois State Police adopted the Model 39 in 1967, an action which helped ingratiate semi-automatic pistols with law enforcement. This publicity helped commercial sales and set the stage for the more acceptable Model 59 with its high capacity magazine at least in undercover or detective police use where the DA feature (and the larger magazine capacity) was considered by many to be superior to single-stack semi-automatics and revolvers of the time period.[1]
The Model 39 was used by Naval Special Warfare units during the Vietnam War.[2] The Model 39 was issued to officers-in-charge (OICs) of MST-2 detachments as their sidearm. SEAL Teams used either the Model 39 without modification or a modified version, the Mk 22 Mod 0, which was called the "hush puppy".[2] The modified pistol had a suppressor with a slide lock (which kept the slide from moving backwards upon firing, thereby decreasing produced noise) The Mk 22 Mod 0 also had raised iron sights, to provide easier sighting over a bulky suppressor. The gun's purpose was to eliminate sentry dogs or guards without alarming the main target.