Looking for John McKay/Mackay who emigrated in the 1850's

Hi there

I'm trying to find any possible connections in Ireland to my great great grandfather, John McKay/Mackay who we believe emigrated to Australia in the early 1850's. By the mid 1850's John was living as a free settler on the Kings Plains Goldfields in NSW, prospecting for gold. Going by his children's birth certificates (all in NSW), marriage certificate (in NSW) & death certificate, John was born in Kildare circa 1825/1826. His age on death in 1901 is given as 75 years. We don't know what parish he was born in, but there weren't many Mackays or McKays living out of the county of Antrim. There was a family of Mackays living in Naas, Kildare in the early 1800's. There was a John McKay who emigrated from Ramoan, Antrim in 1852, so this may be him, but it conflicts with all records that state that he came from Kildare. Any help here would be appreciated. His name was spelt as McKay but there was one recorded spelling of Mackay, also of McKey. All we know about him apart from his family records here was that he was good with animals, so he may have lived on afarm or been a shepherd.

Thanks, Deb