There are a lot of non-fiction books about Kokoda. Perhaps some of the best known are:

Those Ragged Bloody Heroes, Brune P, Allen and Unwin, Sydney, 1991
Peter Brune was one of the first authors to put the Kokoda story into print. It's a very clear account, and an excellent way to get into the history if you don't have any background knowledge.
Kokoda, Fitzsimons P, Hodder Headline Australia, Sydney, 2004
In this book the author has really tried to get inside the heads of the men who were on the Kokoda track. Definitely worth reading.
Kokoda, Ham P, Harper Collins Publishers, Sydney, 2004
This is a very detailed account of the whole Kokoda campaign. There's a lot of material in this book that you will find difficult to locate anywhere else. Paul Ham has done anyone who has an interest in Kokoda a huge service through the depth and care of his research.
The Silent Men, Dornan P, Allen and Unwin, 1999
This is a great text, especially if you want to find out about the 2/14th battalion.
Recollections of a Regimental Medical Officer, Steward HD, Melbourne University Press, 1981
An excellent book. It also has one of the best descriptions of the physical conditions on the Kokoda Track you will ever read.


And, there's nothing quite like getting at the primary sources:

Have a look at the Australian Army war diaries on the Australian War Memorial Website (www.awm.gov.au). Especially those of the 39th, 53rd, and 2/14th battalions. You'll find them in their Collection Databases.