You might try making a detailed comparison with the old Scott Bonnar Queen (Model 16) - see this thread:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=37570#Post37570

I can't relate the details to your mower, a lot of easily recognisable covers seem to be missing from yours, but if by some miracle it is a Queen, you can probably get all the parts you need at realistic prices. There seems to be no market for Queens outside the bowls club greenkeepers, and they are tossing them out these days because of their extreme age (up to 60 years).