From what I read, the aforementioed can is available for my Sniper Rifle at the 188 Trading Post and the Vendortron at Gun Runners. It's been days, maybe weeks with it not in stock. Anyone know the reason? Just a luck of the draw when I show up to the vendors? Could having it equipped help?

Its randomly available. you could just be unlucky. i know that the Vendortron only restocks on sunday and wed if that helps.

It first depends on what level you are. The wiki says that the Sniper Rifle is available at the 188 and the Gun Runners after level 11 so that might be when you can get the suppressor.

LOL No. It is funny that you tried that though... As if showing the Vendortron the weapon in question helps it realise what part you are looking for..

suggestions:
- buy a few other mods and see what the stock is replaced with
- try the women by the NCR truck over the freeway bridge at the 188.
- there might a trader in/around Cottonwood Cove, try them (not sure about his one, I've never seen a trader there)
- keep trying the vendors (it is random so some people get it early others have to wait)

Good Luck!