Could be this one:
https://www.ebay.co.uk/itm/TWO-PIECES-OF-2-PIN-SPEAKER-PLUGS-FOR-VINTAGE-VALVE-AMPLIFIER-/3027846084...
Description shown 2.9 and 2.1 mm Dia. and 8 mm apart.
https://www.ebay.co.uk/itm/TWO-PIECES-OF-2-PIN-SPEAKER-PLUGS-FOR-VINTAGE-VALVE-AMPLIFIER-/3027846084...
Description shown 2.9 and 2.1 mm Dia. and 8 mm apart.