I would like to sell a patent. Do you have a way of advertising it?

Yes. Upon request and payment of a fee for this service, the U.S. Patent and Trademark Office will publish in the Official Gazette of the United States Patent and Trademark Office; Patents, a notice of the availability of a patent for license or sale. For the current schedule of fees, see the U.S. Patent and Trademark Office (USPTO) Web site at http://www.uspto.gov/go/fees* . Please note: Fees are subject to change in October of each year and should therefore be verified before submission to the USPTO. To obtain further information, you may contact the Office of Patent Publication at 571 272-4200.

* see Fee Code 8022 - Publication in Official Gazette
USPTO FAQ - Questions and Answers (27NOV2006)