So you will have a car to get to Radda, you just want to enjoy wine without driving?
The easiest solution generally is to join in with wine tasting groups that drive you out to the wineries, but that is easiest starting from Florence or even Siena, as the tour agencies group people up.
Having said this, Radda is surrounded by vineyards and wineries, and they have the House of Chianti Classico in town which allows you to taste wines from the area and they likely arrange these types of tours. Actually some are walking distance from town, they might actually have a map of the ones that are open and their hours and you can reach them walking without worrying about driving.
Of course, if they don't have tours and you want to reach places that are further away, you might be able to get the services of a private driver. Maybe you can ask the hotel or place where you're staying at and ask whether they have a list of drivers or can actually arrange this service for you while you're there??
