you can go to any ford dealership normally and see if they will order them for you, or I can possibly get some prices for you... just let me know what your actually looking for...shoot me an email and I will reply to ya!
What I had done when I had gotten my White Cobra R's was painted the shitty Bullitt Center cap that had been on there high gloss black and found these center cap decal like things that some lady had been making at the time on ebay! and stuck them over the center cap in the center so they blended in, and then took some clear coat spray and hit them with 3 coats of clearcoat and let them dry for a bit, and there it was, a lil ingenuity on my part...
Here is a pic upclose of the finished product:
http://www.rhythmuniversity.com/donna/Upstate%20Mustang%20Club/Members%20Rides%20June%201/Output/pages/DSC00117.htm