Hi!
I'm from the Netherlands, but I'm not actually living there at the moment, so no tips but a few websites:

For the most up-to-date list of events/workshops/sessions etc. all over Holland (mostly Irish folk, but occasionally Dutch folk too), go to Eltjo's folk page, and check out the 'agenda'.
For Dutch folk music, check out this page , and have a Dutch dictionary handy.
Good luck!

Letty