Hi Catt,
Is it the link to your own local police authority you're looking for? I can't recall INZ having a form where you can apply online for a police certificate but I'm sure some local police stations do have them on their websites.
I came up with
this where you can click on the appropriate area you live in and it will bring up details of your local constabulary (or should do - when I tried it told me there was a gateway error
) , but others did come up.
If you have any further trouble, give us a shout and let us know which area you live in.