Sorry, I don't have any recruiting agency info. I used to be in environmental consulting too, though mostly dealing with contaminated soil and groundwater investigation and remediation.
A while ago I searched on the internet and bookmarked some sites. Many are dead ends now, but the one below might be of interest to you. There didn't seem to be much, though it could be that I don't know the right Kiwi key words like I do in the US.
You could augment your search based on your educational background (e.g. engineer, geologist, chemist). I've got additional info on the geosciences.
Crown Minerals: this appears to be a government-run oil & mining "company". Those sorts of operations always need monitoring or cleanup somewhere.
The
Department of Conservation used to have a "Jobs Available" link, but it is dead now. But you could try them anyway.
The regional councils also use environmental scientists, though that would probably be in a more regulatory capacity.
My OH probably has a huge list of links to job prospects, but it's not on this computer.
Good luck!