There are no ticket agency I believe that sell tickets only for campsites as they always bundle them with overpriced General Admission.
My advice is to
1. Contact the ACO and try you luck. You will have to be very lucky at this stage.
2. Look on this forum from time to time in the sell and swap section.
3. Look on aution sites, but leave this until late as they are always overpriced.
4. Become a Dane.
Good luck KN tickets seem to be very rare nowadays.
