When booking your flights you need to get to Auckland, which is on the North Island.
Our preferred route is with Emirates: London - Dubai - Australia - Auckland. It is 2 stops as opposed to the standard one, but we find this more bearable that two mega long flights!
For those worried about the long flights, we can highly recommend Dubai and Australia as stopovers for a few days. Korean airlines do a nice overnight stop in Seoul and include a hotel, to recharge your batteries in between flights.
When you arrive in Auckland, The Bay of Islands is a 3 hour drive north (or you could fly - to Keri Keri). It's a lovely drive so take your time and explore on the way up. Stop for lunch at the Waipu Pizza Barn - you won't find better pizzas in NZ!
There are lot's of buses that go to and from the Bay, so if that's your preferred option, check out www.intercity.co.nz/ or nakedbus.com/nz/bus/auckland-to-paihia
Once in the Bay, head to Paihia. This is where the wedding will be and the best place to base yourself. See the 'Wedding Details' section for more info on accommodation...