Ground Effects or Styling kits.

You have two different options. Look around at Euro sites like Stillen and other companies that make ground effect kits they usually make kits for american cars as well, you also might want to buy a mustang performance magazine. Second option is the one I preffer. Take measurements of your car and try to find a kit you like from a euro that has simular measurments and break out the fiberglass and adapt it to you car. It will be 100% original and you will be envied by all other mustang owners (not really, but you get questions)

HK

try <a href="http://www.wingswest.com" target="_blank">www.wingswest.com</a> im not sure if they have what you're looking for, but they do have a big selection.

u can try fxdesigns.com
pakfeifer.com
performancetuning.com
ondergrounddesign.com or ondergroundesign.com not sure if theres double d
and search ebay.com automotive for body kits, theres hundreds of them, i know a lot about euros, so just ask me if u need more help