Can anyone suggest how i best try and find a list of immigrants who came to Australia from 1800 to 1900.
Your question is currently a bit too broad as there are so many separate sources depending on state/ dates/ assisted (or not) etc. Could you please narrow your question and/or (- even better -) give name(s) and other details like life event data / family relationships etc.
Anyone with surname of COWIE who landed in Sydney, NSW between 1800 and 1900. That could include convicts, assisted and unassisted people. Specifically a JOHN or DAVID COWIE, but as there are plenty with those names, it is best to get all COWIES and then i can possibly get more leads from their siblings etc.. who may also have come out with them.
Try the NSW state archives: