Here is my write up on front side marker lights. These are as close to OEM that I have seen all the way down to the checkered reflector part. They were very inexpensive, ebay from some ricer outfit in Cali. I think less than $50 shipped.
http://www.moddedmustangs.com/forums/2005/128188-ziza-install.html
http://www.moddedmustangs.com/forums/2005/128188-ziza-install.html