There are few items which vendor don't sell at all, but generally if you have the "right" level (35+), you can find almost all the clothes in epic (it's the higher version available for "random" clothes, apart the "fix" legendary ones...)By "junk" I mean like visually vendor trash level that I would never get caught at wearing. There are a handful of legendary items, but not the clothes that I want. And the worst part is that I know those clothes exist, they just never show up at vendor.
The nexus mods site implied that there are like 4 costume vendors that are "broken", in that certain items show up once, and then never again. Im inclined to believe it. There was a mod to fix it, but I didnt get it working. Some errors.
For this outfit :
I had to skip times about hundred times for the pant to appear in the shop in epic (near River house).
And easily more save reloads for the jacket, boots and inner torso in legendary with max mod slots...
The same for this jacket, hundred of "skip time" to have in epic...
So it's possible, but annoying as hell for sure...