For ticket-ordering from now on, I'd give
Page & Moy or
Just Tickets a try.
You are running a little late for the ACO, so that's your best shot - unless you don't mind Beausejour (a camping site not far off Porsche Curve, but far enough from everything else). Don't forget to book your ferry crossing too!
For all other relevant info you can check
this topic for all usefull addresses and phone numbers.
Good luck!
