Oh you are soooo lucky! New Zealand is amazing. I never wanted to leave when I stayed for a semester a few years ago.
I believe that NZed has a group of orchids called the Sun orchids, many of which are a lovely blueish color. I wonder if those are for sale at all. Ahah...some are native to the country, here's a website with them
New Zealand (NZ) Native Orchids THey don't have any links to sellers, but they've got pics of a bunch of native orchids
I don't remember any orchid places from when I was there...but then again, I wasn't into orchids yet.
Not sure if you're going to Wellington...but it's an amazing and beautiful city, and the gardens there...the Wellington Botanic Gardens are pretty sweet. Acres and acres on the side of a mountain...oh YES there are orchids in there I believe...in a greenhouse, at the rose place! They also have a ton of carnivorous plants in there. ALSO...in Taranaki...well, New Plymouth (also North Island...), there's some botanic gardens, and they have this half-underground/cave like greenhouse, which had probably TONS of orchids in it, now that I think about it. It was sweet. Looking it up...Pukekura Park. Geeze, its all coming back to me. Don't remember anything similar in the South Island....but there are PLENTY of other amazing things to visit there. If you're in Dunedin, do the Otago Peninsula for a half-day or so...see Lover's Leap and the other cliffs, and the world's steepest street...which was pretty amusing. If you have a couple days in Auckland...drive over to Coromandel for a day, and see if you can make it to Cathedral Cove and Hot water Beach.
A huge destination is Milford Sound...but I thought Doubtful Sound was even more amazing. Take a cruise....they have half-day (though it will take you a whole day to do it all anyways, since it's so far off from anything else) trips and overnights. Might be pricey for either place...but so worth it. I felt like the whole world was summed up right there in the Sounds.
I also swam with dolphins in the Bay of Islands. THAT is cool.
Ok...I could go on all day. Point is...there are sooo many things to do and see, you'll just have to pick what seems appealing to you!
Got any questions about anything, and I'm happy to try and answer, though I didn't make it everywhere. I bet you will have a lovely time!