The Leviton electrical socket doesn’t have a Volkswagen part number and was used on the American models only.
The parts manual is saying “Purchase locally”.
You could use a 110/125Volt single socket or a double socket.
In 1965 and 1966 the socket was mounted above the left taillight.
The reverse light hole was used for the socket. 1967 models SO-42 had the socket on the left side panel.
The original Leviton socket is made out of aluminum, the socket is still for sale in America in a plastic version. (Google Leviton model 4937)