All the crap a bout the Louvre notwithstanding I seem to recall being able to purchase the Pass at Charles de Gaulle on arrival. Of course with the main website down and no sign of it returning I can't find that info anymore. All I can find is on the Paris Visitors site that you can pick up a pre-booked order at their office or at the Gare du Nord.
Can you still buy a pass on arrival in town, anyone know?