to be honest I think I am being a bit dim
I tried the 'contact us' email thingy on four or five Aprilia dealers and also on venhills site (none of them got back to me) before dropping in on the local custom bike 'we fix any old Jap bike' team yesterday and the bloke took one look at it and said 'this afternoon ok for you?' Idiot me. Then in a fit of pique as none of the aforementioned dealers had answered my emails I called one up. After ruminating a bit about never having seen a bike like mine anywhere he found the part and said it could be ordered.
In future I will check more thoroughly before jumping on here but it was very helpful to be directed to the carb chaps so thanks for that.
So far I have managed to find a good second hand shock from a chap in Germany, the carb to inlet manifold rubber from the carb blokes plus another on its way from an ebayer in Italy. Local custom guys to do the choke cable plus one on order. I hope to fire it up next week then all the bits for the forks are easily available and I will rebuild them then its back on the road.
I hope.