You can locate the field "gun" for the ARCHIMEDES weapon by entering the Freeside's East Gate and locating the two children chasing each other during daylight. Talk to the one holding a toy gun. You can purchase the gun for 1,000 caps or 20 caps with Barter at level 45 or greater. To use the weapon you must supply the power to ARCHIMEDES II during the "That Lucky Old Sun" mission.
