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.com
http://www.ullmansails.com/

You might also try
www.oxosails.com
www.taipanamerica.com
www.ashbysails.com
www.northorder.com

Bill