Hey! Did ya check between the backseat and floor? that gap dips down a good four inches, that's where I FINALLY found mine.
I got worried also. I had the silver ten spokes with a MALE (closed ended, like an acorn) locking lug.
That means nobody's taking it off without a key.
I had two supercoupes and one prior mark viii, all without keys. The mark viii had snowflakes with center caps like the supercoupe wheels, so I had room, and all the locking lugs were female, so I could simply use a wedge (punch, chisel) and 5 lb. hammer to cut in and slowly get them to turn off.
But on the chrome/silver ten spoke wheels, we don't have center caps that cover the lugs. No place or room for that chisel. Plus they were male and either chrome or stainless instead of soft unchromed steel which means no place to mount the chisel tip even if we did have large center caps. And chances of a socket that will fit over the locking lug and still fit in the lug hole, slim. I know I couldn't find one, using snap on and mac tools.
I think ford has about 105 keys, and my three most local dealerships at the time didn't have a master set, or the key that I needed. And since my car was more than 8 or so years old, they didn't have my VIN number in their database anymore to tell them which key I would need. I wasn't going to order all 105 at $20 some bucks/pc. They wouldn't have sold me a whole set anyways.
Anyways, make sure it's not in the car behind the seat, crawl in and run your hand through there carefully, I checked three times there before my fingers finally 'felt' it, and I have skinny fingers. It was quite the relief after my research. I was on my way to lighting the torch.