The first part of the schematic for the Dart Gun are found at the MDPL-05 Power Station on the northwest tip of the Capital Wasteland. Another part is obtained from Hannibal Hamlin after completing the "Lincoln Memorial" quest for the slaves. The last schematic is found in a locked chest at the Boutique Le Chic in Tenpenny Tower. Parts required are a toy car, surgical tubing, paint gun, and Radscorpion poison gland. The Dart Gun cripples your target's legs. It is very useful when used on fast melee opponents such as Deathclaws. It also poisons your target for eight seconds.