I also live in NL, but am British. To make things more confusing, my DH is German. Again, like HWhisperer, I speak only English, DH speaks only German. LO is exposed to Dutch at kindergarten.
Just keep it consistent, have clear lines between who speaks what, and there (should) will be less confusion separating the two/three languages in your child's head....
My DS's English was better when in London, now the German is catching up. I am pretty confident his understanding of both will end up being balanced.
It is sometimes hard though, trying to work out whether my child is saying 'look' in Dutch (kijk), or 'cake' in English, or biscuit in German-- similar word again.... for example(!) :0) Argh!!
Also, in answer to the original OP, living in SW London, I came across a good number of Dutch/part Dutch families, so I think it should be easy to find others to 'hang out' with. Don't know of any groups though, but am sure there will be some in your area.