In Seattle there is "Second Wind" r some such name, they are a 2nd hand store of all sorts, sails,
winches, motors, books etc. Two places, one in Freemont, the other at Shilshoal marina next to WM. Otherwise, most of the used lofts seem to be on the east coast, ie bacon sails etc.
You might also check the local North, UK etc lofts, as they sometimes have sails too, but not listed online. North has an online used website also.
Marty