This page has the lyrics AND a recording of John McCormack singing "Roses of Picardy." The song starts playing automatically when you go to the page. (For some reason, when I did it, I ended up with 2 copies of the song playing at once, out of sync. I had to cancel one of them.)

Alternatively, you might be able to download this: "http://www.westfront.de/roses of picardy.mp3"