most of the typical wearing parts (chain sets, carb repair kits, brake pads, etc.) are easily available on the market.
We have issues with some dedicated engine parts! Sometimes it is easier and cheaper to swap the complete engine instead of repairing the “old” one.
I expect that some parts like plastic side covers, mudguards, fuel tanks, etc. will never be offered as after market products.
In these cases individual solutions or good, but used parts are required.
Also the exhaust system is causing trouble and there are many, many different solutions out there. Actually we (in Germany) are working on stainless steel downtubes (2-in-2 arrangement) for use with universal silencers.
Can’t see that the aftermarket will supply stuff for our Twins like you’ve mentioned with you car.
BTW: To adjust the valve play you might need shims in a certain thickness. Measure the play, remove the shim, measure it’s thickness, calculate which shim sizes you need and post here which shims you are looking for.
We may help you 😉
Have a look at this document:
Ok, it is in german language but maybe you can recognise what it is all about 😉