Every year in October / November four professional Italian restaurant guides - some say even gastronomical bibles - are published.
Very useful could be also the journal Ristoranti http://www.ristorantiweb.com/
Special PDF Version of FoodService Europe & Middle East 2011/4.
Pan-European Survey: Vegetarian Restaurants Part I. Shifting out of the Eco-freak Corner into Mainstream Society. Page 8-18. Contributing Author: Italy: Flavia Fresia
Some basic nformation offers the printed guide "Viaggia vegan. Guida Italiana. Turismo & Ristorazione. Prefazione di Salvini Simone. The guides costs around € 20,- at amazon.it.
The Michelin Red Guides and the Gault Millau Guides have become widely known as the world’s most respected sources of restaurant and hotel evaluations. But from a vegetarian or especially vegan point of view the problem is that both guides, the Michelin Guides and the Gault Millau are nearly "totally meat obsessed". Michelin Guide Italy - 2300 selected restaurants with only 1!? vegetarian restaurant.
More European and national Restaurant Guides
In German language you find the PDF of a very usefull portrait about veg restaurants in Sicily.