New Zealand Touring Guide: Creative New Zealand offers a free tour guide designed for bigger performances, but has significant relevant advice. You can check the Creative New Zealand website to get the latest version. There are a lot of useful resources at the Creative New Zealand site.
Event Finder is your friend: eventfinder.co.nz. They do online (and hard copy if you want) ticketing and their system is quite good. They also list venues with contact information for those venues. If you don't know where to start, you can have a look at what's in town. You can look at locations that similar concerts, performance or events are being held, and check dates against what else is happening in town to make sure your event does not clash with someone else's.
Music Clubs and Societies are also your friend: A lot of towns (small and large) have music clubs or societies with concert series. In the big cities there are general several, but be aware in the large cities they tend to book at least a year in advance and may be fickle about who they want to host or type of music they desire to host. One good source of information for folk and acoustic music clubs is http://www.kiwifolk.org.nz/clubs.html.The thoughts included in this page are gathered from and the opinions of individuals that are members of the Harp Society of New Zealand. The content contained within may on occasion be out of date, and is offered to provide assistance; however no responsibility is taken by the Harp Society or it's members regarding outcomes.