Go to the Horowitz farmstead and go directly north and you'll see several merc's one of them has the alien blaster
Bullshit. You will only see the mercs if you don't have the Wild Wasteland Trait. As when you reach the place one of the mercs will have the YCS/186 Gauss Rifle. If you have Wild Wasteland there'll be three aliens hanging out there. The mercs will be dead near the rock wall, one of the aliens has the Alien Blaster. And it's actaullay Northeast from the Tumbleweed far, where you get a stealth boy from a nightkin (agree to buy the "Wind Brahmin" right away, otherwise he'll charge all your caps) and can blow all the aliens with a carefully planned pants explosion. (Plant a frag while pickpocketting someone)
Basically, go as far north as you can a bit east of Brooks Tumbleweed farm and you'll see a saucer and three aliens. Don't screw around, just shoot them and loot their bodies. The captain has the alien blaster and ammo.
The first answer is wrong but not as wrong as the second. Go directly north of Horowitz farmstead towards the mountains that border the map. You'll see a crashed space ship on top of a cliff you can't reach, and three aliens below it, where you can kill them. The Alien captain has the alien blaster!
The fourth answer is wrong but not as wrong as the third, U can actually reach the spaceship if U get out of the map near the Brotherhood of Steel SafeHouse, its just hovering & it's EXACTLY like the spaceship thats in the Mothership Zeta Hangar, the 1 that crashed in the Capital Wasteland, but it ain't it... -Chowder
first guy said shit go north of horowitz and zap fucking e.ts
Just go north of Horowitz and kill the Aliens, They're pretty easy to notice and are easy to headshot. The Alien Captain will have the Alien Blaster and Power Cells for it. But don't worry, the Captain cannot use the blaster against you, he has his own laser pistol.