Looking for Any Family Ofjohn Mitchell and Louisa Peat Married South Australia 1849

John Mitchell (b. about 1815 New York, USA) and Louisa Peat (b. about 1830 Nottingham, England) immigrated to Australia separately, Louisa on the ship "Harlpey" with the "Lacemakers of Callis" in 1848. John's arrival is unknown. They had 3 sons, John, James and Thomas in Victoria, Australia, then seems to disappear. Any help would be appreciated.