Hi guys.
Just wondering is there any "lore" in-game (which meaning not by google or wiki, etc. )
that let you know the exact location of some named/legendary weapons?
For example, the Gobi Campaign Scout Rifle can be located through a note in Camp McCarran.
On the other hand, I can't find any notes/messages/quests related to the overwhelming YCS/186.
And it's not available by buying since merchants just don't sell it. lol
( Examples will be "That gun", "THOR", "Medicine Stick", etc. )

So is it possible to access those weapons while sticking to immersion playing style?

As far as I can tell, there isn't any way to tell where most unique weapons are, other than looking them up online or stumbling across them, obviously. THOR is a mod weapon, so I assume that you're playing on a PC. I'm afraid that I can't remember the precise name, but there's a mod that scatters pretty much every unique weapon in the vanilla game to various spots throughout the Mojave and random enemies will drop notes as to where they are. I think that it might be part of NVEC.

Thought this was something else. Though it would be good to name your own modded weapons, there is just nothing to point you in the direction of named items. I would not not bother with them, as they are not as good as being smart about a battle.