Geodati.gov.it lists Cadastral cartography by munipality. However, all of the links to download ("scarica") these files are grayed out. Each file lists a website and some contact information, so you may be able to request these as downloads. They also provide an XML file, so you may be able to add these to a GIS project as WMS layers.
Here's a link to the google-translated page.
If that won't load, go to http://geodati.gov.it/geoportale/ and click on Dati di base topografic e catastali, then click on Parcelle catastali. Here's a direct link.
There's also a map viewer ("Vizzualizatore"). This seems like it would allow you to see the parcel/cadastre layers, but I couldn't figure out how.
I found this site by translating "real estate" (immobiliare), "parcel" (appezzamento) and "download" (scaricare) into Italian, then googling shapefile scaricare appezzamento immobiliare.
I know this isn't exactly what you were looking for, but I hope it helps you get closer to what you need.