The pibroch "The Earl of Seaforth's Salute"? It's not a lament but it might be used as one in your context.

Or, why not use one of the psalm tune recordings from Lewis in the School of Scottish Studies series?

I currently can't get the slow 6/8 march "Leaving Lochboisdale" out of my head, and it would certainly work if played more slowly than usual, but it relates to Uist. (I play it to myself through headphones on the electronic bagpipes on my to work).

A tune from Lewis recycled as a lament elsewhere: #185 in Simon Fraser's collection, "Cha bhas thig air Laoch ach cadal", "A Hero Never Dies", used as a lament for Wolfe of Quebec.