Following a hot tip, I was able to locate a MB ticket at cost last week via Nadine at the Le Mans tourist office. You can enquire, book and pay online.
Worth a try!
Doug
Below are details of tickets available.
Beauséjour 
 46 € 
 8 €
 
 
Bleu nord 
 51 €
 8 €
 
Expo 51 €
 8 €
 
Houx annexe     
 51 € 
 8 €
 
 
Karting nord 65 € 
 10 €
 
 
Tertre Rouge 
 81 € 
 15 €