This book is ideal for someone from overseas who has not done a lot of cycle touring overseas before. It has simple sketch maps but no elevation charts. Available from book stores in New Zealand, and online . It aims to provide all the information you'll need to create your own routes. Lot's of info describing available services, accommodation and road gradients.
Some users say it's a bit too densely packed.
Available from some bike shops and book stores. Top Classic New Zealand Mountain Bike Rides by Paul, Simon and Jonathan Kennett, 3rd ed. This is the New Zealand mountain bike bible. Some of the trips described follow public gravel roads, others are hard core off-road expeditions. Desciptions are consise.