I wouldnt try to fit another type of boats sail to your boat, even a used sail would be waste of time and money. I would take the old sail to sail loft or call one of the popular sail manufacturers - Ullman, North, Quantum, etc
I have an Ullman main that I like - Jay Glazer or Charlie Ogletree could probably help you -
ullman@ullmansails.comhttp://www.ullmansails.com/You might also try
www.oxosails.comwww.taipanamerica.comwww.ashbysails.comwww.northorder.com Bill