Almost any sail will work, the question is how well it will work. For reaching around, you can hoist pretty much anything and have a good time. If you want to go well to windward, it is a different case.
I would go and check out the boat for structural integrity of all parts. If it is OK, buy it and have fun with the sails on it. Then start looking for something better. An ad on Tornado.org and http://groups.yahoo.com/group/Tornadocat/ gives good odds on tracking down OK sails.