I got mine from the original vendor. They were listing em for $49... only had 50 or so I believe. The jacked up prices are from people selling these original ones.
Everyone knows the Mustang is a Ford, and everyone knows it's a Mustang when they see it. Except for the pony in the grill and on the windshield, it doesn't have any Mustang designation either. It does say Ford on the fake gas cap. Ford didn't need to put their name all over it. It's an icon that's unmistakably recognizable.
According to my research over several weeks, Shelby isn't selling them to anyone. You must have a Shelby VIN and a reason why you need a new set; IE a police report.
Where:
There are a few sets out there, I estimate ~100 sets (nation wide) were sold before Shelby stopped open production. You can find them online if you look hard, but expect to pay $200-300 for a set! It's difficult for me to spend that much for two pieces of painted plastic.
Why:
So, you are probably wondering why Shelby would do this- as the Powered By Ford emblem could be used by any Mustang? Simple- to cut down on clones. This is the same reason why the Shelby hood scoop is also hard to find.
Alternatives:
1) The prototypes and very early Shelby GT models actually used the factory GT emblem. You could just use this one as a viable solution.
2) Scott Drake, under licensing from Shelby, still makes and sells the Powered By Ford emblem used by the Shelby Cobra models (from the 1960s). It isn't exactly the same, but it is the same design. You could use this one if you like the old school look more.