Without proper details, it's difficult to check resources for you, but there is plenty you can do for yourself - and you might recognise something that someone else might not.
First up is BDM Online - Historical Records (https://www.bdmhistoricalrecords.dia.govt.nz/Home/
You can purchase copies of registrations on that site. Be sure to get the printout, not the legal certificate, for family history purposes. (I explain why at http://archiver.rootsweb.ancestry.com/th/read/NEW-ZEALAND/20...
Do check at https://www.bdmhistoricalrecords.dia.govt.nz/dataCollected/
to see exactly what information should have been gathered at the time of the event. Some of the earlier registrations (such as marriages before 1880) don't contain sufficient data to be considered useful to us family historians, so it's a waste of money to buy a copy.
If you don't want to order online, or are dealing with more recent events that aren't on the historical site and don't have an iGovt registration, you can order via ordinary mail - go to Births, Deaths & Marriages (BDM, http://www.bdm.govt.nz/
) and locate the appropriate form. Print the form, complete it with what you know, and send it off with your payment. You can also call and place an order over the phone.
If you are a member of the New Zealand Society of Genealogists (NZSG, http://www.genealogy.org.nz/
) enquire at their Certificates Collection before making purchases at BDM. If they're holding what you're looking for, it is much cheaper.
Before this "historical" web site, we had the older annual indexes on microfiche. These are still around, and are still useful. Look around at libraries and genealogy groups near you for them, or if you're an NZSG member you can make use of their free Research Service for lookups.
Another useful site is Archives New Zealand (http://www.archives.govt.nz/
Anyone can walk into an Archives NZ office and request to view a file they hold. Files are not moved from office to office for your viewing convenience - you have to go to where it is held. Check on Archway for viewing restrictions, and if there are any there will be information there about how to get permission if it is possible.
If you cannot get there yourself, someone else could visit for you. Ask on this board if you need assistance, and someone may be able to go and take photos for you. There should be no charge, as there are no entrance fees and no material costs with emailing digital photos.
Alternatively, you could pay a fee to Archives NZ and they will send you a copy of the file.
Also check Family Search (http://www.familysearch.org/
) Click on the link "Australia and New Zealand", then "New Zealand, Immigration Passenger Lists, 1855-1973".
Hope this helps. :-)