They are different than the regular GT ones in that the lights have a ring around the bulb socket and the retainer grabs the ring. Its kinda backwards of the regular ones.
I wish I had a picture to post, but I don't have the original lights or retainers anymore. I have some aftermarket OE style lights from DEPO on the car and they are lousy in terms of quality and beam pattern. The repro lights use the regular retainers. I picked up a pair of OEM Ford ones on Ebay that are pretty nice, but the retainers didn't come with them.
I have looked at various Mustang parts places, and I only found them listed at two places. They say that they are on backorder. Ford says they are discontinued.
I don't see what was wrong with asking if anyone had them. I've seen that asked numerous times on several forums. That is what forums are for is helping others. I just thought someone might have some laying around.