If you go to
http://www.tc.gc.ca/aviation/activep...torysearch.asp and enter G73 under Model Name, 8 Mallards show up, but none with the two registrations you entered. CF-YQC was a PA-32R and C-GASY is a C182P
However, this database only goes back to 1982, but there is a link to the National Archives of Canada if you need older information.