McCormac/k - Maher families

Helen McCormac is my name and I am reserching great great grandparents, Patrick McCormac/k or McCormick and Nancy Maher, lived in Holycross,Co Tipperary had a son John and a daughter Ellen, John and Ellen sailed to Australia to Port Adelaide about 1860 and John maried  Catherine McDonald- parents-  Archibald McDonald and Julia Pannan - Julia was also born in Newtown. Ireland.  John McCormac/k his marriage certificate states his name as written by John  ( McCormick) however over the generations and looking a handwritten certificates, McCormack has ben spelt thre ways. I am hoping to trace his parents, they may have lived in Holcross CO, Tipperary when John was born about 1843.  John's death certificate states he was born Holycroos, Tipperary.  John died, 1903  - Mildura, Victoria, Australia.    John and Catherine's marriage certificate indicates Thomas Quinn as their Witness.  He also arrived with John on the Ship Nugget, about 1859-1860 to Australia.  I am desperately trying to locate any information regarding his parents or siblings.  My family in Australia would be most grateful.