You'll spend far more time right now trying to figure out where the bancomats are than it will actually take you once you're there to either ask your RS guide (who will definitely know) or to just ask someone on the street "Bancomat?" and they'll point you there. Spend your advance time adding value to your trip, not collecting useless information. (I don't mean that to sound as harsh as it sounds. It's just that there are many things that make sense to plan out in advance and this isn't one of them.) IMHO, of course.
And, yes, they are everywhere. But they're called "bancomats" in Italy, not ATMs.
And BTW, you're going to have a great time!!