rivers on the north of south island

Hi we came from Czech republic and want to paddle here. Right now we came to south island where we should have seasonal job in few weeks. Is there some river which we should visit? we are close to Nelson and in Europe we paddle rivers 4-5. We have Mystics.
Are there some kayakers we can join? Because we are just two with one car.

thanks
Simon

Look on this website. There is a River Guide section. When you get to the area you will meet other paddlers.

ok, we have 10 free days so we decided to move to westcoast because we really want to paddle.
Could you recommend us some rivers there(probably close Murchinson). is there something else than Buller?
is there some grade 4 which has water?