There are several large used sail vendors. Bacon in
Annapolis and Minneys in SoCal are two that come to mind. Determine the proper dimensions for your main and then check their websites. You will likely find several candidates.
In the past I bought from Bacon and found their condition descriptions to be quite accurate, even on the conservative side (ie,
sails were better than I expected), and I've heard the same about Minneys. Prices range from perhaps 80% of new for unused but second hand down to 10% of new for pretty beat up
sails. IMO the best values are in the slightly used range, with prices ~50% of new.
Good luck!
Jim