The only version of the song that mentions Thoro or Thorro, so far as I know, is Child's example J, which Roberto has already mentioned. It was noted from Marion Miller, Threepwood, Melrose, apparently by Thomas Wilkie, presumably in the first decade of the 19th century or a little earlier. Not the text we have here, though.

The hill is almost invariably just a "high, high hill" without a name; the only instance I know of where it is identified is in Jane Turriff's set, where it is referred to as "yon Tenniesbank", this being a localisation to the Tinnis Burn area, near Newcastleton. (Jane Tuffiff, Singin is Ma Life, Springthyme SPRCD 1038, 1996).

I should imagine that this is a collated rather than traditional text. Since lyrics are not printed in the CD insert, you will probably only get guesses in answer to this question unless you ask Sandra.