Board Thread:FarmVille (game discussion)/@comment-71.60.197.213-20130709151409/@comment-75.34.25.63-20130710080126

It looks like it is no longer available in the market. So the only way you could get one now is if one of your friends/neighbors has one in an aviary and throws an aviary egg containing the pyro duck into their newsfeed, and you are able to snag it. (If they are even still doing that because my newsfeed hasn't worked in about a year now.) Most likely, you are just out of luck.