Well, I found this:
The valour of the Highland Division is recalled in the pipe tune "The Heroes of St Valery" composed by Pipe Major Donald MacLean of Lewis. He is said to have based it on a folk song he heard at St Valéry. The tune was first played at the Highland Brigade gathering in Edinburgh in 1947.
at: http://www.iain.laird.btinternet.co.uk/51st_Division_at_St_Valery.htm
So, I guess we keep looking for the "folk" tune......