Personally, I would not bother to buy used sails from another C 27 as they are probably just as worn out as the ones you already have. If you have sails & they are just tired or ripped, perhaps they can still be repaired by a local sail loft. Or if there's no sail loft around you, then buy a used commercial sewing machine & fix them yourself.
When you have the money saved, it would be better spent on new sails that aren't already blown out, & too baggy from wear & over stretched from too many over zealous teenagers hauling them up, & cranking the devil out of the seams with a halyard winch!
The biggest improvement you can make for a boat's sailing performance is to invest in new sails, but it seems like its the last concern of many sailors. Mainly because its such an expensive, but worth while investment. If you have no sails at all & can only afford used, then look up Bacon Sails in Annapolis online. They sell a large number if used sails from their loft.