Good to know that you have been using a Ginge mower all these years – they were certainly built to last!
As for spare parts, as far as I know (from when I did research) Ginge mowers were made to their own design so parts may be hard to come by now.
I’d have a look through anything to do with Al-Ko as they now own Ginge, you never know what may turn up and I’m unsure if any of the modern Al-Ko mowers are of the same or similar design or carry over some parts – exploded diagrams might help there.
Otherwise it may be a case of seeing if a new spring can be manufactured by someone local, or see if a similar mower comes up on an auction site which could be used for spares.
Research can pay off some times as, after 18 months, I’ve just found a brand-new double-drive gear (£14) on a German website to mend a broken hedgetrimmer.