Tracey
Borders FHS completed the MI's for Kelso parish church some years ago. I've checked, and photographed the stones in the churchyard for a new edition of the MI.
Unfortunately, I don't have a record of George Dickson (d. 1848) or for a Christian Leishman - there are some stones which are either illegible or have fallen, which haven't been recorded.
Sorry, I don't have anything more useful for you
Elma