According to John Mackay's death certificate (his wife, Marion McLennan being the informant) he was born at Inverness. We don't now the exact date of his arrival in Australia other than he lived in NSW for 7 years and in Queensland for 31 years until his death.
His cousin also named John, arrived around about the same time and does not show on shipping records either. That's because he and a friend jumped ship in Melbourne to try their luck on the goldfields.
There was a good story (with photos) about Captain John published in the Mackay Daily Mercury, Monday Jan 27, 1986 as an Australia Day Feature. I understand you can still get photocopies of it from their office. Unfortunately the beautiful headstone in the photo was broken in two when last I saw it in 1990.