I'm tempted to attempt a Dutch ride at some point; I've got friends in Bergen NH; are there any starting around Alkmaar? or at least between either Hoek or Ijmuiden and Den Helder? as that would work best for fitting visiting them with it!
The Maasland 300 a few weeks back started just 10km from Hoek van Holland, infact you cycle past the ferry terminal on the return leg. It also went all the way up to Alkmaar. There was a 400 ride that started in Amsterdam, and last week there was a 200km from Overveen (17km west of Amsterdam). I don't know what rides will run next year, but of the rides left this year, there is a 200 in November from Bergen Op Zoom (south of Rotterdam, almost Belgium). But I think that's the closest to the areas you're talking about.
However, do remember that public transport in .nl is pretty damn good. From Alkmaar you can easily get a train to Maastrict for any of the BRM's there, or to Utrecht, and thence to Bunnik for the rides run from there. The Boekelo rides are harder by public transport from the Randstat (I have a hotel booked for the Boekelo 300 in October).
Are you thinking of doing a ride this year, or next?
J