I've been playing New Vegas for a while now, I have 3 profiles that have made it close to the end mission and several others that I abandoned by level 10 or so. Not once has a sniper rifle suppressor presented itself in the inventory of a vendor.

I see on the wiki page that it should occasionally be available from Gun Runners and the Arms Merchant at the 188 Trading Post. I have checked these two places twice per in-game week throughout my 3 character playthroughs and have never seen the sniper rifle suppressor. I got the carbon fiber parts, as well as all the other mods for the other weapons.

I'm trying to hang up my Ratslayer, even though it's a monster early on in the game, but I seem to be cursed with the absence of this mod.

Has anyone else had this problem?

Check the gun runners, if they don't have the suppressor, save your game then quit the game completely, reload your game and the gun runners will have restocked there inventory, rinse and repeat.
Level 10 may be to low to get the weapon mod though.

I'm not at level 10, I'm level 28. I have 3 characters that are around lvl 28 and none of them have seen the sniper rifle suppressor. I mentioned that I had several other characters that I abandoned around lvl 10, but I'm not using any of them now.

I have tried to quit the game and re-load several times. I know about that trick . I also know where the mod is supposedly sold, but it literally NEVER appears. Not once in 3 characters that have reached at least lvl 28 has it appeared.

And I am looking, trust me, it's not there. What I'm asking is if anyone else has had this problem. I'm not new to the game by any stretch of the imagination, I know how things work and when the vendors refresh their inventory.

In my current game the 188 Arms Merchant gal has three Suppressors and two CF Parts in her inventory, and I never use the damn Sniper Rifle.

Did I buy your copy by mistake?

I've just about given up on it. So strange though, I have no idea what could cause my game to seemingly omit something. I'm just going to stick to a silenced 12.7 pistol for now.

Sometimes, you just have really bad luck with weapon mods.

Sniper rifle suppressors can be bought at 188 or at the Gun Runners. If you try enough power-shopping tricks (realoads, three-day sleeps, etc.) enough times, you should be able to get a good roll at one of those two.

Or you could just stick with Ratslayer for silent work

Don't give up, you see I had the same thing but with 40mm Grenades...

If I may suggest go to the Gun Runners store with the Vendatron, save your game, exit the game and restart... Once you restart you just need to use the wait function to wait for every Wednesday and Sunday, I recently found that these are the days that the Mojave stores restock their supplies....

It may take a little while to randomly spawn the parts you are after but keep at it and you will find them...

Go to the 188 post with the Sniper Rifle equipped. I don't know if it's coincidence, but when I first went there with the Hunting Rifle equipped, she had all 3 mods. With a Sniper rifle equipped, I got both mods.

I had the same issue with the hunting rifle scope on my first playthrough. My level was well into the 20's by the time I was able to find one for sale, and by then I was using a fully modded sniper rifle for all of my long range killing and was completely used to it. So my hunting rifle never got used.

On my current game, Alexander had the scope for sale when I first talked to him at the 188 on my way to New Vegas. Needless to say I snapped it right up, even though I hadn't even gotten a rifle yet.

play an energy weapons only character... then you will find plenty of sniper rifle suppressors...lol

mods always show up for weapons I am not using on my current game.

But you might try waiting 3-4 game days. (If on hardcoe, go to your hotel room & bring food - sleep and water are supplied in the room)
I try both dealers at the 188, gun runners, Blake, novak, the fort, goodsprings, or silver rush (e-weapon mods)
That's 8 merchants to try, and they restock every 3-4 days.

Unconfirmed: I think the game KNOWS.... buy your suppressor before you get a sniper rifle.