Hi Richard,
Are you still looking for your birth family?
If you are, have you tried looking in the phone book for likely candidates? There is one R SANDERSON listed living in central Wellington.
www.whitepages.co.nzWith you being born in 1966, it might be possible for you to find out the names of some of your siblings from the birth indexes, especially if they were born 1960 onwards. Prior to 1960 the indexes only give the name, year, and folio (reference) number. From 1960 the mother's first name and any middle initials were included.
The indexes are on microfiche, and you may be able to find a set at a genealogy/family history group near you in Australia, or at your State Library.
The suggestion to work through Jigsaw is a good one, I hope they're able to help you. :-)
Kind Regards,
Wendy Howard