There is a surprising amount out there really, considering only a small handful of New Zealanders were directly involved in the conflict. Mark Derby has written and edited a few books and articles on the wider topic - I'm not sure they're what I'd call cutting edge scholarship, but they exist. See in particular:

• Kiwi Compañeros: New Zealand and the Spanish Civil War (Canterbury, 2009).
• Petals and Bullets: Dorothy Morris – New Zealand Nurse in the Spanish Civil War (Sussex, 2015).

You can also download Susan Skudder's doctoral thesis on New Zealand responses to the conflict here.

Amirah Inglis' book on Australians and the Spanish Civil War might be a useful point of comparison. Very few of the broader overviews of the international dimensions of the conflict will even mention New Zealand, but if you can check out our booklist on the Spanish Civil War here for recommendations if you need them.

Hi - we as mods have approved this thread, because while this is a homework question, it is asking for clarification or resources, rather than the answer itself, which is fine according to our rules. This policy is further explained in this Rules Roundtable thread and this META Thread.

As a result, we'd also like to remind potential answerers to follow our rules on homework - please make sure that your answers focus appropriately on clarifications and detailing the resources that OP could be using.

Additionally, while users may be able to help you out with specifics relating to your question, we also have plenty of information on /r/AskHistorians on how to find and understand good sources in general. For instance, please check out our six-part series, "Finding and Understanding Sources", which has a wealth of information that may be useful for finding and understanding information for your essay.