I agree with Donna, likely not a problem in finding last minute hotels as they are on booking.com and whatnot systems online... while most family-run farmhouses and B&Bs are a little behind and not online, at least not with an automatic booking system so you need to contact them ahead of time with ample time to get a reply. I always recommend if you want a particular place, to write to check availability and book ahead. In Italy, not even hotels in the city or countryside have "vacancy" signs to indicate they have rooms, so it all depends on either local tourist offices having that info or checking online what is available for last minute bookings.