The Technician has given me a mission to get som siphon units but I can't find any indication of where to look. Can anyone help please?

I assume this is the mission from the Exocraft Technician where he sends you to find Armadium. Your exocraft can scan for resource depots (d-pad down on a game pad, then select the exocraft's signal booster from the menu). Once there simply shoot the containers to get the required Armadium.