For used sails you can go two routes that I know of.
1. Contact your local sailmakers and see if they have some in their loft. Many sailmakers will resell customers sails for them when they buy new sails.
2. Check out used sail brokers or Sail Swaps on the net. Some that I know offhand are Atlantic Sail Traders and Sail Swap Texas. I picked up a spinnaker for a 23 foot boat for $250 CDN rather than the $1400 it would have cost new. You can find these sites using your search engine. Like everything else in life you should use a company that somebody you know has dealt with ...
3. Be sure you really know what new sails cost before you decide to buy used. Used sails are OK but not always in the same shape as new. I recently discovered that two sailmakers locally charge vastly different amounts for a new main sail. One quote is a Cruising/Racing sail that is 60% the cost of another from a well known source.
Best of Luck