Bladefire, I can't help you with MB tickets, but are you aware that you only need one ticket per vehicle for MB and not one ticket per person?
If you are taking down more than one car, it is probably easier and cheaper to buy two car park tickets (see other threads) and then try to locate one MB ticket for a vehicle to take onto the camp site.
Just a thought - happy hunting (can't interest you in a BSJ ticket can I?