Hello Helen
I may be telling you what you already know but David Scarlett came from Karamea in northern Buller, NZ and was a member of the Brethren Fellowship, often referred to as Exclusive Brethren these days. He was the third of fifteen children and there are lots of relatives still living in Buller.
Im not aware whether you are a member of the Brethren youself, but if you are, you will know that there is a series of volumes written about the Brethren during wars. If you aren't a Brethren your local library may be able to get it for you. Its called At the Front and it runs to about 50 volumes I gather but the one you want is Volume 16 which has a chapter on David Scarlett.
I tried to read the inquest report but the link wouldn't open for me and neither I nor our local library have a subscription to Find my past.
i can possibly give you a bit more information on the family if you want it. If you're interested, send me an email.