How do you get alien guns in borderlands?

The first alien gun I got was in the mission 'Is T.k ok' at level 22 in the arid badlands. Go into the house and you complete the mission. Go passed T.k Baha and to the door at the back of the Hut. Open it and go outside. There will be a gun crate. Open it. I found my 101010 Cannon in there. It does 586 damage and infinite ammo but has low accuracy, fire rate and a slow energy recharge. Then, get your best gun out and go out the other door. Seven Phycos (I'm not sure how you spell it) will come at you. And if you were good the day before maybe the Badass Phycos might come and MASH your car up and your characters face in.