Regulatory Agency Demilitarization Act This bill prohibits a federal agency from purchasing or using a firearm. The bill excludes the Departments of Defense, Justice, and Homeland Security, the military departments, the Nuclear Regulatory Commission, the U.S. Capitol Police, the Bureau of Diplomatic Security, and the Central Intelligence Agency. The Government Accountability Office shall submit to Congress a report that includes specified information regarding each federal agency that has specialized units that receive special tactical or military-style training or use hard-plated body armor, shields, or helmets and that respond to high-risk situations that fall outside the capabilities of regular law enforcement officers.