If you unequip your weapon and become totally unarmed then use the weapon repair kit, a little amount of health will be restored.

Prior to patch 1.2.0.314, the recipe required an additional 1 scrap metal, 1 wonderglue, and 1 wrench.

Finding this code gives a constant supply of weapon repair kits even after returning to the Mojave Wasteland, making weapons very easy to maintain. Also, there is a code for them in the police station, sitting on top of a filing cabinet.

In the same terminal where you find the code for the demolition charge in the Puesta del Sol service route, the code for weapon repair kits can be found here.

If one leaves the area and returns later, additional items may be taken. However, only one of these items can be grabbed, as the disturbance caused by grabbing one forces the other items under the car, making them disappear. There are also 2 Duct tape and a skill magazine.

One can be found in a police car at the Poseidon gas station.

If the trait Wild Wasteland has been taken, this location is next to The One.

The super mutant camp in the northeast corner of the map, north of The Devil's Throat.

One is at Jack Rabbit Springs by the skeleton and two metal poles near the pools of radiation.

The Boomer Munitions Manager in the Mess hall & munitions storage at Nellis Air Force Base sells up to 5 kits (average: 2, refilled every 3–4 days) if you have a positive reputation with the Boomers.

At Mesquite Mountains Crater in Hell's Motel, on top of the wooden shelf nearest to the door, next to a D.C.

At the Nipton general store, on the bottom of a tipped over shelf next to Boxcars.

In Southern Nevada Wind Farm on top of a shelf.

In Jean Sky Diving to the right of the set of lockers.

In the Searchlight fire station, on a shelf on the first floor, the same room you enter into when you first zone in.

At Mojave Outpost, given by Jackson after completing the quest Can You Find it in Your Heart?.

The Gun Runners also sell the materials to make it on the workbench.

At the Gun Runners on a shelf, for sale.

In Goodsprings, in Victor's shack, on the table in front of you when you first enter.In Jacobstown, in the Jacobstown lodge take the right hand stairs down the hall to the last room on the right side before the bathroom on the middle shelf near some communications-electronic equipment.

In the Abandoned Brotherhood of Steel bunker in the main room on a metal shelf.

The dropbox in the Abandoned Brotherhood of Steel bunker spawns 100 Sierra Madre chips and 1 voucher (worth 1000 chips) every 3 days, allowing the player to buy 55 Weapon Repair Kits every 3 days making this an invaluable source for the kits, provided they found the Vending machine code.

Other than being crafted, weapon repair kits can be found in the following places

How to repair guns in fallout new vegas