Genuine Old West holsters may not have been what you picture.
Western gun belts hold a certain allure, a type of mythological majesty. A gleaming nickel single-action sixgun riding in a leather western gun holster on the hip of a deadly gunfighter cuts an iconic image.
While most genuine cowboys didn't carry their single-action revolvers in fancy leather holsters with lots of tooling and fancy embellishments, there is a long history to gun leather.
Today, lots of leatherworkers still make hand-tooled, western-style leather gun holsters, for cowboy action shooters, as well as for people who just want to own a real cowboy holster rig of their own.
The first handguns were single-shot muzzleloaders and they were usually stuffed into the same belts from which sword scabbards were hung.
When the first revolvers were introduced, namely the Colt Walker and the Colt Dragoon, they were large and heavy guns that were meant to give calvary a multi-shot firearm inside 50 yards. As such, the first holsters were mounted on saddles in various ways.
Gun belt holsters started showing up in the 1840s for small, single-shot pistols, like pepperbox guns and early revolvers. They were simple open-top affairs, some with open toes as well. By the 1850s, holsters were made with cover flaps for protection from debris and weather. This style of holster was used through the Civil War and beyond.
We started seeing what we think of as a western holster emerge during the Gold Rush of the 1850s, and was known as the California pattern. Western holsters by the 1870s were generally made of thick leather, and to get at their gun faster, people started tucking the top flap into their belts to keep it out of the way. Naturally, holsters began being made without the flap. People who spent most of their day in the saddle also preferred cross-draw holsters, as they held a revolver more secure while riding and were easier to draw while seated.
However, the idea of a leather fast draw holster that hangs low from a gun belt is mostly fiction. This is known as a buscadero-style holster. You'll find stories that Mexican vaqueros used this kind of holster in the 1890s, but it's almost certainly an invention of Hollywood for the earliest westerns in the 1920s. Of course, a holster could be made any way someone wanted, but a low-slung holster would not have been common.
Also, very few people would have kept revolver cartridges in loops on their belt. If they didn't use a bandolier, most people carried extra ammo in a simple leather belt pouch. In reality, having a chance to reload a single-action revolver like the Colt SAA under fire would have been rare. The frontiersmen who carried multiple pistols didn't do so because they shot them with a gun in each hand, they did it because reloading wasn't a real option.
So even though what many think of as genuine leather western-style holsters never actually existed in the Old West, you can still buy a western gun rig for a western style gun. After all, you're not making a historical documentary.