Parking permit required

We seem to have forgotten to sort the parking permit, and it looks like we may have left things a bit late.
Last year bought a Rouge parking permit online from the ACO site, good car park for the price. Unfortunately the site is now saying unavailable (sold out?).
Is it possible that the ACO sell a certain number of tickets in advance and then keep the rest for purchase on the weekend? (I seem to recall hearing something about this last year).
There was absolutely loads of space in Rouge last year.
Any advice greatly appreciated as we have everything else sorted, but without somewhere to park we are somewhat screwed.