This is a schematic weapon. Shishkebab is built from a motorcycle gas tank, motorcycle handbrake, lawnmower blade and pilot light. One of its schematics is found with Vance, who gives one to you after the Blood Ties quest. Lucky Harith the wandering merchant has another. There is a final set near a workbench in a Red Brotherhood Outcast shack, to the southwest of SatCom Array NN-03d. The shack does not appear on the map, but is at the base of the hill the array is built on. Every schematic you obtain increases the condition of the weapon when it is built. Its damage is 40 plus 10 fire damage over five seconds.
