Do you know when / where / who he married. When / where did he die. You have a birth certificate for one of his children. What does it give for Gordon's age...birthplace....occupation etc.
You can do a lot of this yourself. Use the NZ BDM site to find birth for Gordon, 1905.
Using mother's name, find her marriage, 1913, and birth of child, 1914.
Mother has a distinctive given name, and you can see her birth, 1887.
Gordon's mother, Ovitt Elizabeth PETHERBRIDGE died 1956.
Does this sound like your family?.
Poverty Bay Herald 6 Aug 1913 p2 marriage notice.https://paperspast.natlib.govt.nz/newspapers/PBH19130806.2.6
Use the newspaper site https://paperspast.natlib.govt.nz/
to find the BOX and PERTHERIDGE families.