I am wondering (if the probate and naturalisation records aren't enough) if contacting an historical society near Leigh might be helpful.
It is a bit of a guess which one may hold information on that area, but here are a couple:
Matakana Museum and Equestrian Centre, 1 Omaha Flats Road, Matakana
Warkworth and District Museum, Parry Kauri Park, Warkworth
Otherwise, local libraries sometimes have a biographical/historical collection and certainly newspapers (though not many have theirs indexed so that a person can easily be found in them).
I did have a look in the Rodney District Council cemetery database and nothing showed up in the way of possible family members (ie if he got married etc).
It does look though from that death print out that there was no one really close to him to fill in the personal information of parents names; and they certainly were not aware of a wife. That he was not returned to Leigh for burial may indicate that there was no one to contact regarding this decision also.
The age though does look good.
[Just as an aside, the bay below Leigh is called Matheson's Bay.]
