According to the NZSG CD "New Zealand Burial Locator v2" (
http://www.genealogy.org.nz/Sales_11.aspx?CategoryId=11) a John St. Clair GUNN was buried at Kaikoura in 1907. He was 54 years old at the time, and the information comes from te Kaikoura County Burial Register transcription on the NZSG Cemetery fiche (fiche N01.11).
There is no record of a monumental inscription there, so there may not be a headstone.
There is no Hester/Ether GUNN listed on the CD.
You may like to check Archway (
http://archway.archives.govt.nz/) the online index for Archives New Zealand (
http://www.archives.govt.nz/). There's a probate listed for this man, and you may find other items of interest.
Files held at Archives can be viewed for free at the office holding them - they're not moved around the country for viewing convenience. Or you can pay to have a copy sent to you. Details are on their web site.
Hope this helps. :-)
Kind Regards,
Wendy Howard