www.car-part.com or Ebay.
Have you tried Carquest or Autozone or NAPA?
Have you checked out http://lincolnvscadillac.com ? You can get almost any question answered about your MARK VIII there and the community will find just about any part you could ever need.
Looking for a Used Mark VIII in your area?
CarGurus has 53 nationwide Mark VIII listings and the tools to find you a great deal.
Search Lincoln Mark VIII Questions
Lincoln Mark VIII Experts