I see what you mean (on both counts!) I hadn't made the connection between the well-known tune and those words; now that you mention it, though, I've certainly heard it played and/or sung often enough. I expect I have a recording of somebody or other singing it, too, but my record collection is not well organised. At any rate I find it in Bruce Campbell's Orain nan Gaidheal vol I, though there in tonic sol-fa which I can't read.

As you'll know, the 'common' tune is also called 'Orange and Blue', and that name seems to date back a fair bit. I believe that a form of it appeared under that name in the fourth part of Gow's Repository (so early C19 at least), but I only have the first three. At what point it became associated with 'Brochan Lom' I can't begin to guess, but I see that it is or was commonly taught in schools and seems to be a staple of the Gaelic choirs; so that form will largely have supplanted any others (such as Miss Tolmie's example) in the popular consciousness.

In 105 Songs, Lucy Broadwood refers to "another tune to similar words in Puirt-a-beul" (ed. Keith Norman MacDonald, 1901, containing material provided by Miss Tolmie). I don't have a copy of that; it would be interesting to see what it was.