I looked up the information on the 75 edition of Ford Car Parts (aka MPC) and there is only one radiator used for your application, C9ZE-8005-K, as Jeff stated. That is a unique application, apparently only your specific one and a Boss 302 with A/C.
I recommend you look it up in the MPC available in this forums' library just to familiarize yourself with the MPC for any parts questions you may have in the future.
As to radiator shops, they are getting fewer and fewer as time goes on. I recommend finding a Mustang specialty shop, or any other type of classic car shop (Corvettes come to mind) in your area for a radiator shop recommendation.
Jim