A couple of people have reported turning up at the ticket office and being lucky in getting tickets for next day.
When we arrived it was sold out. But I was told that if I went up past the venue there is a small side road which runs for a few kms to a Chateau where the admin for Puy takes place. I jumped on my motor scooter and found the place (closes at 5pm). I went up to reception and the very nice girl on reception looked on the computer and hey presto, we got 2 x tickets inc the night show for the next day. Marvellous.