Derick S. Thompson's 'An Introduction to Gaelic Poetry' published by Victor Gollanz, London 1974, mentions that 'Coinneach Odhar' by 19th century Isle of Lewis bard Iain Mac a' Ghobhainn, "a poem about the legend of the Brahan Seer, is a modern heroic ballad. It is influenced distantly, mainly in matters of nomenclature, by James Macpherson's work, but weaves legend and imagination to make a new blend, It shows narrative strength, and has startling clarity, and a power with words, here in the main simple, terse vocabulary."
Unfortunately Thompson doesn't quote from this poem, although he gives lines in translation from Mac a' Ghobhainn's more politically oriented poetry. It was common for Gaelic poetry to be set to tunes. If I should come across the 'Coinneach Odhar' poem in my further reading, I'll let you know.