I might have a pair from a PH2 somewhere, haven't a clue whether they're 'old' or 'new', or even how much it matters in the real world especially if it's not working for its living every day, but they'll need servicing (I can arrange that if required). Otherwise they shouldn't be too hard to find, there must be plenty still in service/recently retired.
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
Many thanks for the help. Examination of the numbers suggest the engine is an AV Series 2 rather than a PH1 as I originally thought. Automarine Diesel Services of Portslade West Sussex are getting me the parts I need.