These sunglasses are worn by a mannequin after heading straight through the entrance to a red brick building (a store called "Lucky's"), which is located southwest of Tenpenny Tower near the southern edge of the game map.
pcps3xbox360 The shades can fall off the mannequin and land on the mannequin stand, where picking them up may be difficult. Exiting and reentering the area may cause the glasses to move, but they can always be found on the bottom of the mannequin stand after a few tries - look hard, as they are nearly invisible. They will fall as soon as the cell loads on PS3. [verified]
If the shades have fallen, try loading the auto-saved game of when you entered Lucky's. If this method worked, the glasses will be on the mannequin's eyes. If not, they can usually be retrieved by: entering third person and crouching near them, then rotating the camera AWAY from them, until "take" message appears (face the pedestal and turn toward the counter; to the right of stealing Med-X, next to the toolbox); first dislodging them with explosives; or both.
If going the route of dislodging with explosives, find the milk crate (movable) and manually set it between the toolbox and the mannequin stand. Place several frag mines in the box and then chuck a grenade nearby. By elevating the explosives, you will have a better chance.
If the glasses are sitting on the round base between the mannequin's legs you can jump onto the counter stand on the toolbox. Crouch and use the third person view to move towards the wall. It is possible, even likely, to get stuck here and have to try again if you can not jump out after getting the glasses. At some point you will move down to the base and pointing the the back wall underneath you the glasses will be able to be taken.