Tracking down my Italian ancestors! (Naples)

Buonasera!

This is a little out of place on an expat site, but I figured I'd give it a go anyway....

My family has been on a hunt recently to track down our Italian ancestors. We just made a break through today when we were able to find my maternal grandfather's petition and acceptance for naturalization for the USA in Protected content . This file confirmed the port he sailed out of (Napoli), the year he arrived, and most importantly, his birth place (San Giovanni in Fiore). To my incredible dismay, we also confirmed that he renounced his Italian citizenship, which I believe exempts us from obtaining dual citizenship. However, we'd still like to continue the search, and since we have been able to put together quite a bit of our family. Unfortunately, we have come to a halt with one of our great aunts, so I am here, trying to figure out how to continue.

My question is this: does anyone know of any resources, in Napoli or anywhere closer to the Province of Cosenza where I may obtain any family records? There is still a large chance that we have family living in San Giovanni, but since there is such little recorded in that area, we do not know where to continue. Any and every advice is welcome!

Grazie tutti!!

Ashley