Identify soldering iron plug and required socket
The connector is a cheaper version of the XLR called an Automotive/Aviation GX16 Series Plug. 
There may be many manufacturers in China, but here is one: http://www.hzconnector.com/product/60388845390-800546210/Silver_Aviation_Plug_4_Pin_16mm_GX16_4_Metal_Male_Female_Panel_Connector_Pack_Of_5.html

They are very commonly used on soldering Irons and CNC/Stepper motor connections the -4 eg GX16-4 indicates the number of pins. They come in 2-14 pin variants.