Here's one of many places to find a Theme Camp:2012 Theme Campsviewforum.php?f=283
If you see one that interests you specifically, send them a nice email or Private Message.
You will also want to join the Netherlands regional group email list, as they will probably have advice for you:http://regionals.burningman.com/eu_nl.html
Remember that the theme camp experience is optional. Theme camps involve a certain amount of work and a fee, in return you hopefully get satisfying work giving the city an experience of some kind, & some support (usually shade, often showers or certain meals, etc, etc). If you camp on your own--which is never truly alone, you will have many neighbors--you must take care of yourself and each other, but your time is totally your own.