Good second-hand gear can often be found at Cash Converters. I got my Alpinestars there for $40 - almost as new, couldn't believe my luck when I found they were exactly my size. they also have leather pants, jackets, gloves, etc.
You could also try the shop in Onehunga Mall - I think it's called The Budget Clothing Shop or something like that. Big range of leather gear - new and used. Got my new leather pants there for $200.
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