These events take place every year. For other events, such as local fairs and food festivals, as well as other local events, there is no calendar yet because it's really early. In fact local events, such as typical "sagre" or food festival, are generally advertised and communicated just 2-3 weeks before they will take place.
The best thing to do is you go directly to local tourist offices and ask for the events' calendar. I also suggest you read our blog about Tuscany on Fridays when we publish a post on the best events in Tuscany, together with suggestions for spending the weekend in Tuscany. I also recommend you have a look at our Tuscany events' calendar that we update on a regular base.
I hope these suggestions helped you. Don't hesitate to come back with any question