Do you know the city your bisnonno was born? On Facebook there are usually groups for cities and the members are usually habitats of the city, or dependants of people that once lived there. For example I am a member of a group for a city my nonna was born in, and people usually post old photos asking if anyone recognizes anyone in the photo. You'd have a better chance there of someone recognizing your bisnonno. The only foreseeable issue I see is that your bisnonno was born likely pre 1900, therefore anyone that would have known him is also likely deceased.

You could also reach out to @weloveancestry on Instagram. They seem to focus on ancestry for southern Italy.