First up, just a couple of cowboys. Most Western costumes do not come with trousers, so on the models the most common choice of trouser you are going to see is a pair of blue jeans. Historically, during the era, most men did not wear blue jeans. The most common fabrics were wool blends or for cavalry types and laborers you'd likely find duck, a cotton canvas material (makes good protective gear). Boots NEVER come with the costumes and the guns are always sold separately. More than half of the costumes do not come with hats. Chances are the costume is a duster or vest and a bandanna, and for this you will pay around $70. Still, these are good generic "Western" options. You could build something Weird West or Steampunk out of them.
I don't name these things. Somebody working copy at the catalog stores has that duty, and man are they bad at it. This is your basic, low effort, Clint Eastwood job. Except he's carrying a rifle, and the poncho is shitty. Take a look at the description I have thoughtfully boxed for you. This "costume" is a damn poncho and shirt WITH ATTACHED VEST. That's it. What vest? I'm sure it's in there somewhere. Extra points for the model not shaving for a few days to complete the sadness.
"When ah say 'draw', slap leather, ya owlhoot!" I looked up several outfits that were labeled gunslinger or gunfighter and this was the best representation I could find. It's pretty much an amalgamation of the ideas we have of fictional gunfighters. You have the fancy waistcoat and simulated frock coat of a man of some refinement, plus that dickey to give you the illusion of a cravat or something. But then you have jeans again and the hyper-Wyatt Earp mustache, which is not included. Oh, and neither are the guns, of course. The gun belt is included, however. The more I look at this the more I want to see this guy get drilled in the street at High Noon. If we put a few bullet holes in the waistcoat with some dried blood and did a corpse makeup or a skull we'd have a decent little Weird Western outfit going here.
It's another gunslinger, actually. I'd prefer this one with a tin star on the chest. Make him into a town marshal or something.
Those are Gamblers. Frilled shirt, fashionable waistcoat and fashionably cut jacket. These men arrive by stage, hang out on riverboats, and like to live well, enjoying their winnings. They project a sense of having money, which is always welcome in a poker game, and may be more than what they seem. Chaps are for work, riding horses and sichlike. When you think gambler you should think fancy duds, a hidden derringer, and a slick attitude, not Wyatt Earp up top and then, ahh screw it, gimmie some chaps and a rifle, I might need to ride the range. It's like a cowboy came into town to drink and whore and raise Cain, as they do, and then bought a new shirt. It's sad. So sad.
Finally we have this guy. Bartender Wild West Costume for Men. Seriously, where do I get this part-time job of naming costumes "professionally"? This stunning costume comes with a bow tie, they are very specific about that. There is a vest with attached shirt, because it would have been too much of a chore to attach the bowtie, and there are arm garters (because what bartender WOULDN'T have arm garters) and an APRON (I can sense your excitement) and holsters. Now our clever model has put a couple of bottles of pisswater in his holsters to make this a "funny" costume. Please note that the beer mug and mustache are SOLD SEPARATELY. Look, you might get by without the mug, but consarnit, you are going to need that jaunty stache. This whole costume confuses me, which is why I saved it for last.
I'm trying to think of why you'd ever want to dress up as the barkeep at the Whore and Cuspidor Saloon. Has this guy ever been cool in a western? He gets about 4 lines, and two of them are "What'll it be?" and "We don't want any trouble here."
So I wracked my cabeza and thought, maybe, just may-be you want to throw a Western Themed Halloween Party and you want whoever is serving the drinks to look authentic, which he will in this outfit (or her, I'm not being sexist here...but she must wear the mustache, that's de rigueur), but that's it. If you are hosting why would you dress as Short-Tap Bill? You'd go the full fancy saloon owner route, wouldn't you?
Other than that, I got nothing. There's nothing cool about being a postman or the guy that works at the livery stable or the telegraph operator.
Now undertaker has possibilities. I'd go that route. Good luck finding the components though.
Keep them pumpkins rollin'.