Be prepared to get annoyed. Escudo is a very rare spawn and you're just as likely to be waiting if you stay in one room as you will be moving throughout the zone. To make matters worse the Arm is not a guaranteed drop, so even if you kill 10 Escudos you may not necessarily receive 10 arms. Another way to obtain the arms is to use the Trinity Level 2 Mission Lobbies and do them with a group. Escudo spawns in this mission and will drop arms more often than the normal spawn.