I thought it would be usefull to compile a list of selling sites, dealers etc in Italy for sourcing obscure parts for the older models.
Here’s a few for starters, feel free to add any more that you have come across. I have used Stornello for my search, but just swap that for what ever model you are looking for
https://www.subito.it/annunci-italia/vendita/usato/?q=Guzzi+stornello++
https://www.bakeca.it/annunci/ricambi-accessori/?keyword=guzzi%20stornello
And a few shops