West Coast Lambretta Works
Great American site with lovely downloadable PDF catalogue.

Casa Lambretta
Vittorio Tessera really knows something about Lambretta's. A rather static site but could be a starting point. Gives also nice spec's listings on most models in English an Italian. Don't forget to visit their nice Lambretta museum with every model made on display.

Weston Scooter Parts
Nigel Cox, the author of the book 'Lambretta Innocenti An Illustrated History' is perhaps the best known Lambretta owner in the UK. He also runs the Lambretta museum and shop in Weston UK.