Even quite small villages have an Office of Tourism and they are usually an excellent source of information, although not infallible. They have lists of all the accommodation and eating in the area, including cost and facilities, and can help you with what is available further on.
You can strike trouble if you are about to cross into a new department, because Offices of Tourism are organised by department, which means that their knowledge of adjacent departments can be almost non-existent. However they will usually ring the office in the next department to help you out.
In some places the Office of Tourism’s information in its own local area is surprisingly poor, as their lists are out of date. Evidently the operators of places that are going broke have more on their minds than informing the Office of their demise.
On the other hand, some places have been dead for years and are still listed. Because you are so reliant on the information from the Office of Tourism, it can be disastrous if they are wrong.
Our worst experience was in the department of Charente, where every piece of information we got from three different offices was wrong.
This culminated in a gruelling 38km walk beside a highway in 38ºC heat. It took us several days to recover from this and we vowed never to return to Charente (a vow subsequently broken).