Although not done anything about mine. I did see the guys do replacement canvas and booked marked for further investigation. http://carhoodsdirect.co.uk/index.php?_a=viewDoc&docId=2 Not taken it any further at this stage but def interested how you get on as feel it is something I need to do next 12 months.
Correct as far as I know everything has to be replaced, mechanism, frame, hood etc. I know Emblem sourced a original Maser kit and fitted it to an early Spyder, parts bill alone was around £5k plus days of labour getting it all to fit and work properly.
If it just needs a new canvas there are specialists who could probably make you one from scratch, these guys are well renowned within Alfa circles http://www.coburnhoods.co.uk