I think it's safe to say that everyone knows someone who loves the Lord of the Rings, or they love the movies themselves. I happen to count nearly my entire family in the "love" camp, which is a good thing because I had people to see the movies with, but was not so great when I told them I was going to New Zealand. All of a sudden, I had a list of Lord of the Rings-related items to buy, and only a small period of time to search for them between all the activities I was doing!
I didn't have the time or the energy to search in Auckland, so Wellington was my first port-of-call on the Lord of the Rings front. Unfortunately, I could barely find any souvenir stores in the Courteney Quarter of Wellington, much less stores that sold Lord of the Rings memorabilia! I thought that since Wellington was the headquarters of the movie, and Peter Jackson's workshops, that there would be plenty of merchandise available. I also thought that since the Courteney Quarter was the one that contains the Embassy Theater—the site of the huge, 100,000 person strong premiere for Return of the King in 2003—it would have plenty of opportunities to find anything LOTR-related. I was wrong.
I went into at least two stores that had "Lord of the Rings T-shirts!" or "Lord of the Rings merchandise!" signs in their windows. However, when I asked the shopkeepers about said T-shirts, they looked at me like I was crazy and told me they had run out of those about 2 years ago. Then why do you have the signs in your windows? That's an awful long time to "forget" to take down a sign.
I ended up empty-handed after my trip to Wellington. Even on a future visit, when I found where the souvenir stores were hiding in Wellington, I still did not find all that much LOTR gear. My advice to anyone that is searching for anything LOTR--and I would think, even 3 years after the Return of the King, that would still be a rather large number--wait until you get to the South Island. Christchurch had infinitely more souvenir stores in general, and at least 2 or 3 that offered T-shirts and guidebooks. Queenstown had an entire store for the Lord of the Rings. This store had plenty of collectibles and T-shirts, but was ridiculously overpriced. I was happy with what I found in the large chains (Aotea NZ, for one), and I think my wallet was much happier with what I found there as well!