You are seeking records during the period of the gold rush. Many people who settled in Vic arrived via South Australia, including my gg grandmother. She was unable to find a passage to Melbourne. Of course the reverse happened as well. My OH's gggrandfather and family arrived Victoria and journeyed to SA where they settled. Many Cornish miners emigrated to SA and the lure of gold in Victoria caused a great many to travel to Victoria, especially to the areas around Ballarat and Bendigo.
Have you searched the shipping records listed in Austalian Resources - South Australia at the top of the board. I can find a couple of Richard HARVEY's arriving SA but they emigrated with wives. One who was single was a butcher from Devon. Nothing that appears to be your man.
Are their parents noted on the marriage certificate? Edward is noted as Richard's father on his death reg and only father simply as CANNING on Margaret's.
Were any parents witnesses?
What was Richard's occupation?
Where were they married?
The headings of the columns on a marriage certificate for the period are usually
Residence and then
Present and
Usual. I haven't seen a marriage cert with former address. I would suggest they had arrived in Vic not long before they were married otherwise their
usual addresses would have been in Victoria.
According to Margaret's death registration she was born c1833 but you have said she was born 1835 according to the marriage certificate. Info on death certs is not reliable. Should would have needed consent to marry. Who gave consent? Perhaps we may be able to find a parent arriving in SA ie if they emigrated.
All their twelve children were born at Ballarat.
Their death certificates should note the time in Australia and each state should be listed individually ie if the informant had the knowledge.
Cheers

Cando