dear as these are discontinued products here in pakistan,,so to restore it you will have to take the restoration route,,the route which everyone folows,,search in all kabar,second hand markets in ur city,, post adds here and on other websites,, try to find alternate ,,may be kisi our cheez ma issi tara ka shocks use hova hoioun,, search for its part number to find something rewlevant,, search for others n google wh have restored it,, their u will get some idea on how to solve ur issue,,
non availabilty of parts is a fairly common issue in restoring old bikes,,, but alternatives always exist,,
also post the exact model details of ur vespa so u may get ssomeones response,,
ask other owners of vespa about it,,
have u checked custom shocks?? heard some people in markewts make springs of custom specs,,may be u can get some info about such ppl and ask their views about ur issue,,