Try some of the hotel web sites for bookings:
www.inter-hotel.com
www.citotel.com
www.hotelformule1.com
www.ibishotel.com
You can also obtain lists of hotels from Tourist Information Offices and some will even book for you.
Someone said to us during a trip last year that we wouldn't be able to find anywhere, that everywhere would be booked up because of D-Day celebrations but it was bollocks, we had no problems at all.