So we're not really any closer to finding the true origin of the song, apart from Mike's post and I am aware that Neil Colquhoun had a lot to do with discovering (writing) a lot of NZ's 'traditional' folk songs. Many years ago (about 1965) I bought a couple of the NZ Song Spinners records, one of them being Songs of the Whalers. No, the Wellerman song isn't on it but the blurb on the back is interesting. I believe they recorded it in 1959 or 1961 and by 1965 I think the group had disbanded. It's a Kiwi records EP - M31-1, put out by AH and AW Reed. It says "The four women and six men who form the Song Spinners group function as a 'workshop of song' each contributing ideas for the arrangement and presentation of the songs of early New Zealand in which they have a strong collective interest."
The members of the group were: Audria Beddie, Sybil Hewitson, Lorna McLeod, Barbie Colquhoun, Jack Murphy, Mathew Davies, Don Yeates, John Godden, Paul Gillet, Trevor Tasker, Neil Colquhoun and.......Arthur WELLER. I don't know if he was related to the Weller brothers or if they just researched NZ history and found the name.   
I wonder if they found any of the above sources and tried to work on them? But it wasn't until later that Neil put more work into it and put it all together?
Robyn