I would try the Tourist information office and then the Mayors office.

The chateau at Tours is accessible from the road via a gravel approach from inside the gates. The castle itself is now an art gallery inside, where they joined the remains together, so outside the best view of the original towers is from the street or garden. Inside the gates, there is an information board on the gravel but there is an area of grass and trees too, nice in the summer. Watch out for the nearby plaque on the wall about Joan of Arc. Enjoy