All 8101 Italian communities are now included in the geonames.org data base as third level administrative divisions ADM3. The twenty regions are ADM1 and the 107 provinces are ADM2. The admin code ADM2 is the two character ISO code and the ADM3 is the six digit Istat code. The first three digits of the Istat code stand for the province.
The data is from GFOSS Italy (Geospatial Free and Open Source Software) based on an old data set provided by Statistics Italy Istat (Istituto Nazionale di Statistica).
The data set from Istat dates back to 1991 and GFOSS in particular Niccolo Rigacci have added the new Provinces and fixed issues with names like wrong accents. They have also setup a media wiki installation to edit and maintain the data. Here the page for Altino with back link to the corresponding geonames entry.
GeoNames Blog 