Have you tried Green Sales in Cincinnati, OH? They specialize in NOS Ford parts. If they don't have it, they will share the part number and provide suggestions of where to try next.
Another suggestion is to try those Mustang parts catalogs as they often share many similar parts. I have had good luck with Mac's and Classic Industries. Their websites are awesome, and they also mail free catalogs upon request. They are nearly as thick as a Sears, Roebuck, and Company catalog! :-)
Good Luck! Happy Motoring!