Hi Trevor
Where do you live? I could possibly help with a few of the things you require - send me a message. You can get new pistons for the S6 from JP Engineering in Adelaide - they have the dimensions, as I sent pistons to them to be copied. I think that the London Douglas MCC has had some more silencers made up, the downpipes would be easy enough to get fabricated. My nephew has to get some made up for his restoration - perhaps we could get another set made up, or even more if the club wants to have some in stock? The carburettor will be harder, but I have seen them on eBay a few times over the years. I hope this helps.
Cheers, Graeme