Angus and Catharine Mcleod of Achiltibuie Ross Shire

angus mcleod b1829,altandu married catharine mclean, achiltibuie b1833 in 1855.It has been written they went to nz in 1859 with two children,following catharine's brother donald and his wife isabella in the same year.
for the life of me,I still cannot find a trace of them,angus and catharine, either here in scotland or in nz.
I like to think,maybe it is possible they went to north america.!