Duncan's father will be either a Duncan or Archibald. His mother will be an Elizabeth or Jean.
There is a natural birth of a Duncan at the sheiling of Fandui, on the hill north of Fortingall Kirkton, SW of Pitkerril to an Archibald Campbell of Balnoe, Kinloch Rannoch and Elizabeth McCallum of Fandui 10 Feb 1784.
There is a birth of a Duncan to Archibald Campbell and Elizabeth McDonald in Logierait 19 Aug 1771.
(Only child)
There is a birth of a Duncan to Duncan Campbell and Elizabeth Malloch at Moirlannich, Killin in 1768.
(1 of 7 children) Naming pattern of children does not match. Not this couple.
There is a birth of a Duncan to Duncan Campbell and Elizabeth McLaren at Ardeonaig, Kenmore in 1780. (Only child)
If his birth was recorded, it will likely be of these couples. The first one is more probable than the others, based his father being in Rannoch and mother being in proximity to Pitkerril.
If there is a missing child birth or a previous marriage, then the above could be incorrect.