I have an idea, but need someone who can write/read Italian. Below is a link to an Italian Association of Jewelry Designers. Might be worth a try to contact them for information on registration numbers.
I just contacted a goldsmith and fellow gemmologist in Rome and there was a book named "I marchi nazionali" published by publisher: River, Via pizzolati, 104 - 36100 Vicenza - Italy. http://www.river.vi.it
His is a 1999 version and 5 days ago he contacted them for an updated version, but they will not publish it anymore.