Hi Rodney,
You may like to make enquiries at Archives New Zealand (
http://www.archives.govt.nz/) about your father. If he was in a "home" for any length of time there may be a Child Welfare file (or similar) on him.
My grandfather was born in 1905 to unmarried parents, who left him in foster care by the time he was five months old. Eventually he was made a ward of the court and placed in an orphanage, until he was old enough to leave and get a job.
His Child Welfare file contained all sorts of information, including the correct names of his parents - his mother told a few fibs when she registered his birth (but just enough of the truth to know we were on the right track when we did find their families) so my grandfather never knew his parents' names.
You're unlikely to find any mention at Archway (
http://archway.archives.govt.nz/), the online index for Archives NZ, so write to them and ask for their assistance. Tell them everything you can - you never know what may help them find a file.
Hope this helps. :-)
Kind Regards,
Wendy