There are plenty of markets in Wellington in August, and on Sundays.
Here's a link to a summary of some available: http://www.wellingtonnz.com/shopping/wellington_city_markets
The Habour City Market is very good for different foods and the odd stalls and is held on a Sunday. The Underground Market is more of your crafts etc and is on a Saturday downstairs in a car park along the waterfront.
A new one that has just opened is the Wellington Night Market and is held on Friday nights in the Left Bank Arcade (off Cuba St) and has food and random items. http://www.facebook.com/WellingtonNightMarket
If you're looking for retro clothing or random trinkets, I'd suggest checking out the second hand shops which are scattered all over the city.
Recycle Boutique (http://www.recycleboutique.co.nz/) and Paper Bag Princess (http://www.paperbagprincess.co.nz/) are two second-hand, retro clothing shops.
Hope this helps and enjoy your travels :) almost 6 years ago