I am a grandson of William Ambrose Brown McNamara, born in 1882, whose parents were David McNamara and Ellen Sullivan. Grandad Will married Honora Connell and had six children of whom my father was the eldest.
All my brothers are with me at the moment visiting. One tells me that our Aunt Lucy's story was that David came in from Australia, having jumped ship. We have records which show that Ellen Sullivan arrived in NZ either on the "Glenmark" or the "Matako". The info on the 'Matako" comes from an obituary in the Christchurch Press 22/9/1937.
Info re the 'Glenmark' comes from a note written on a copy of that obituary written by a daughter of Jack McNamara, Erica Hopkinson, who was David and Ellen's second son. According to cousin Erica, Ellen arrived on 21 January 1865 having embarked on the 'Glenmark' in the UK on 29 October 1864. Ellen came from County Waterford.
Like you, we have not found an entry point for David or Ellen. I have found in an Irish Census the fact that a Bernard McNamara and a Catherine Quinn both lived in the same road in County Down near Downpatrick which fits too well not be taken very seriously as referring to our great great grandparents who emigrated on the 'Bluejacket' in 1866.