Gee, I see we've had a lot of requests over the years for sheet music for "Siege of a Nation." I wondered why no lyrics had been posted. I found a YouTube recording of the song here:https://www.youtube.com/watch?v=lszi0EsOJbQ.
It's an instrumental piece, so there are no lyrics. There are lots of lyrics sites offering lyrics for this song, but they tell you that they don't have lyrics available.
In 1984, Soodlum published THE FUREYS & DAVEY ARTHUR SONG BOOK - 26 Golden Greats by Ireland's Leading Folk Group - used copies are readily available at booksellers. I wonder if this song is one of the 26 in the book.
The Fureys have a Website, http://www.thefureys.com/ - it might be an idea to contact them and ask if they know where to get sheet music.
-Joe-