Hello, and Welcome!!
I'm not sure if you have the complete part numbers--which if you do, you might be able to "Google" the exact numbers, and see what comes up.
I did find a couple of leads--
http://www.parts123.com/parts123/yb.dll?parta~partsort
http://motors.search.ebay.com/mustang_Emission-System_W0QQsacatZ33605
But, you might want to pook at the latest Hemmings Motor News, or their Muscle Car magazine, although expect premium pricing there.
I might be able to look up those numbers for you, and I'm willing to bet that they were also used on the Fairlanes, Cougars and Torinos, all in '68, as well.
Perhaps someone else may be of some help for you.
The best of luck!
Paul N.