Which one? The Dione Sidhe song (http://pocketbard.wordpress.com/master-song-list/the-rubber-duckies-of-dione-sidhe/) with the chorus "all the rubber ducks go quack, quack, quack" is to the tune of Cruiscin Lan, which is very popular and you'll be able to find it all over the internet. (You can start here (http://www.chivalry.com/cantaria/lyrics/cruiscin-lan.html).)

The other one, (http://pocketbard.wordpress.com/master-song-list/the-sign-of-the-duck/) about the raising of the cooking house, doesn't have a tune, because I suck at coming up with original tunes. So that one is just recited. (Unless you can find someone who can make a melody out of it. It's in simple ballad meter.)