I don't have a main for sail, but you might check www(dot)baconsails(dot)com or www(dot)northsailsdirect(dot)com. Bacon sometimes has used sails and you can click on your boat model and it will list what they have in stock with something close to the right dimensions. If you don't get many hits, try searching on the Catalina 25...the rig dimensions are very similar. North Sails will be more expensive, but you could go with a stock Catalina mainsail.
Hope that helps a bit.
Happy days!
Jack
Bella - V2620