yes there is no reason you shouldn't be able to.
No, you can only craft, find or buy the dart gun in Fallout 3.
All around best gun for me would be 'This Machine'.
The unique gatling laser in Fallout New Vegas (The Sprtel-Wood 9700) can be purchased from the Gun Runners provided that you have the Gun Runner's Arsenal DLC.
alien blaster but ammo is hard to find after you have it all and its at the alien crash site
Gun Runner's Arsenal.
Fallout New Vegas is a role playing game.There are several powerful weapons available to find or to buy.The Sniper Rifle is one of the better weapons.
South of Freeside's East Gate and north of NCR Sharecropper's Farm.
That is just something wrong with your disc or something.
The only one I can think of is the Sleepytyme, with the gun runners arsenal pack
All of Fallout New Vegas' DLC's have been released; no more are in production. The DLCs are: -Dead Money -Old World Blues -Honest Hearts -Lomesome Road -Gun Runner's Arsenal -Courier's Stash If you want additional content for your game you could try out some mods. The majority of Fallout New Vegas Mods can be found in the related link.
Unique weapons cannot be modded like regular weapons. 'That Gun' is already a modded .223 pistol, you can't add any other weapon mods to it.
You can buy it from the Gun Runners, and if they don't have it; just wait for 24 hours and check if they have it, if not again, keep repeating.