I'm on my second playthrough, 130hrs in, Lvl 30 and none of the vendors who stock weapon mods has had the silencer for the 10mm pistol all game!

I remember getting one quite early on my first playthrough from Goodsprings or Novac. I know the 12.7 pstl has one (I've got that) but I'm on a mission to have a fully modded version of each weapon in my gun rack and this is the only mod I'm missing.

Anyone else had any mods that never seem to come up?

(and I'm on the 360 so adding with console isn't an option)

Ha. I wish I found one my first playthrough. My best mod was the Night Vision for my first Varmint rifle. I loved that thing. I would have also loved a silencer for my 10mm.

I found one in my second playthrough almost immediately. Of course - this time - I'm playing a Melee/Unarmed character. Go figure.

My first playthrough they appeared around level 8 or so and disappeared a couple levels later.....so this time I bought the first one I ran across.

Thats why I bought every mod I ran across whenever I had the caps.

Rarest mods:
-Gatling Laser CF Frame
-Gatling Laser Focus Optics
-Fatman Little Boy Kit
-Plasma Caster HS Kit
-Hunting Rifle Custom Bolt
-Trail Carbine Forged Receiver
-10mm SMG Compensator
-10mm Pistol Silencer

Not much help, but keep looking.

I know Old Lady Gibson is a great place to check in periodically for mods.
There's a guy called Alexander at the 188 Trading Post that's usually under the bridge and if you have a Guns skill of 40 or more he's got a ton of mods and ammo.
I have no idea if this would be anywhere to look for silencers but at Mick & Ralph's in Freeside talk to the guy who sells the guns (I keep forgetting which is which, the one who sells the weaps is usually in the back) and if you have a speech skill of 30 or more and answer "no" to whether you are with the casinoes or not he'll open up his "goodie" room, which might open up some mods.
Cliff Briscoe might ocassionally have a few mods too, but I keep forgetting.

If none of those people have anything, they're bound to have something.

My last play-through I saw those all on the gun runner vendor constantly.... and my character was built for only using explosives!

Save in front of a vendor, exit to the main screen, reload and their inventory will be different. Rinse and repeat until you find your desired mod. Gun Runners is the optimal choice for this trick.

I'll try the re-loading trick, cheers

Thinking back it might have been that guy at the entrance to the fort who had it last time. The Legion have hated me for most of this game so I've not been able to visit him for a shopping spree.

Cliff Briscoe has both Gun and EW mods. I've gotten 9mm SMG drums, extended barrel for hunting shotgun (adds to ammo capacity), laser rifle beam splitter, and something to increase the speed of plasma pistols from him. If you see a mod and have the money, buy it. It may be gone when you get back. I think there is a bug with the varmint rifle silencer. Both times I tried to buy it from Chet my game froze and it wasn't there when the game reloaded.

got mine at gun runners and ive seen em severl times there since

Can't answer your question. I got mine almost immediately this playthrough. But I'll tell you what I've NEVER found: the Sniper Silencer. I'd give my left nut for one but I have yet to find even one.

BTW has anybody noticed how wimpy the sound of the silenced 10mm is? It's this anemic clicking, like you're firing a toy gun. Should be a cool "pew pew" sound or something. Makes me afraid to put one on my sniper rifle should I ever be able to find that mod.