This year we contacted a Dutch ticket agency, by email and asked them if they had 15 MB, the guy replied they ran out. They were charging 90 euro/ticket, which is not overinflated. I had a brief discussion with him and he was sure he could arrange something for us. So I asked if he could provide 60 MB tickets and he said he could most likely get that amount. That goes for any campsite by the way.
If their is enough interest, I could contact him again and see what we can sort out for next year. No garantuees from my part that we can actually get what we want, but at the same time we could all put a seperate order in at the ACO and see what works out best.