Marine Energy Systems in Coomera QLD may be able to help with aftermarket
Yanmar parts for legacy engines like the QM series.
https://www.marineenergy.com.au
In the past I have sourced QM
parts (rings, bearings, gaskets etc) from Hoye Tractor Parts in
Texas USA without any problem. Note, the
2QM20 engine is based on the Yanmar 2TR20 tractor
engine which was fitted to the YM 2000 tractor. The parts are interchangeable and IIRC, the part numbers are identical.
It seems they are now trading as 'Tractor Parts ASAP'
https://www.tractorpartsasap.com