Most common are Inland and Winchester. Here's a
link.
I'm not entirely certain when M1 carbines became collectors' items as opposed to "a cheap semi auto you can buy from the guvmint." Common versions run around $400-$500 nowadays, but Rock-Olas can be a couple of grand, if you can find one, which you can't.
I
think that in the late-80s they were still just cheap semi-autos, though, so getting a Rock-Ola from the CMP would be a matter of luck back then.
Honestly, not many people mounted scopes on their M1 carbines. Not that it couldn't be done- you'd have to get the receiver tapped first, but that's pretty simple gunsmithing. But I haven't seen many.
If you want night vision, maybe he got his hands on an
M3 carbine? I'm not sure if CMP ever sold them, though. Well, actually, no they never would have sold the M3 because it's fully auto, but some surplus dealer might have sold the scope and accessories, which would be easy to mount on an ordinary M1.
There were literally tons and tons of cheap surplus military ball ammo available in the 80s for both .30-06 and .30 carbine. You could buy it by the pallet. But, as you have mentioned, the stopping power of .30 carbine ball is limited. The Israelis load soft-points and swear by them.
A good varmint gun would be a Mini-14, and they're already tapped to mount a cheap Bushnell scope. That sounds more like this Sommier guy. Are there GURPS stats for it somewhere? Hell, if the
A-Team used them they have to be awesome, right? :)
EDIT- Yeah, the Mini-14 is in
High-Tech.
ANOTHER EDIT- Nowadays there are
scope mounts for the M1 that just required you to remove the rear sight, but I don't know if something similar was available in the 80s.
YET ANOTHER EDIT- Ha! Yes!
Weaver made drop-in scope mounts. You can see one in the pic of the commemorative model on that page.
EDIT AGAIN- Nope, I was wrong again. The Universal (aftermarket non-USGI) carbines
came tapped for scope mounting, so that
Weaver mount wan't drop-in. It still needed a tapped receiver. But, again, that's pretty routine gunsmithing. And would indeed look very hillbilly, which seems to fit your character concept.