Give the ACO a ring , they can speak english . Drop who the company are etc and ask to book for those many tents . They will probably reserve you a place , although you maybe limited to Beausejour .
Another CA member may try and reserve the space for you when they arrive, as most seem to arrive really early .
Otherwise try gettting places from a tour operator , or club , like Merc Benz UK ( owners magazine ) . I have never used a tour firm , others may have details and i am sure they will post a reply . If you get really stuck try Gilles a member who lives in Le Mans , he may know of something else.