A Pair of Dead Desperados, I

 is an unmarked quest in Fallout: New Vegas.

Quick walkthrough

 * Activate the gun case at the Vikki and Vance Casino, giving you a message saying it is empty.
 * Talk to Primm Slim and convince him the gun is missing
 * Volunteer to find the gun and return it.

Detailed walkthrough
A remarkable thing to be seen when entering the Vikki and Vance Casino in Primm, is an old getaway car in the middle. It once belonged to Vikki and Vance, two "notorious" robbers. Walk around the car, read the plaques, and take a look at their costumes. Primm Slim can also give you some background.

In order to initiate this quest, you must inform Primm Slim that the weapon is gone, then pass a Science check of 50 and get the Primm Slim corrupted memory block. You will receive a transcript from Slim of a couples' conversation which points towards Westside. To pick up part II of this quest, head north of New Vegas to the large shack which is Wins hideout.