The components are available from most electronic parts suppliers. A skilled technician will be able to fit the components inside the housing of the jack connectors (We can recommend Neutrik NP2C(mono) jack connectors as they offer space for the components and superior strain relief).
Relay 1 open and Relay 2 open = More Drive Relay 1 open and Relay 2 closed = Drive Relay 1 closed and Relay 2 open = Clean Relay 1 closed and Relay 2 closed = Clean
With thanks to Mr. Martin Sund