My maiden name is Cairnes....and although my parents say our ancestors came from Ireland - I have often seen it listed as a Scottish name. I often see the name spelled Cairns...but you spell it the same way we do. I don't know much about my Great Grandparents...except that they lived in Philadelphia in the early 1900's (they were Irish and evidently drank too much). My grandmother married Matthew Cairnes in Philadelphia in the late 1920's.
Good luck in your search!