I found this post from Muscle Car Blog News to be pretty informative:
The Hertz Corporation is proud to announce that it has contracted with Kruse International and Dyno Marketing on an exclusive basis to manage the public auctioning of Hertz's inventory of its Limited Edition 2007 Hertz SHELBY GT-H MUSTANGS' A strictly limited run of 500 2007 GT-H Convertible Mustangs were produced by Carroll Shelby exclusively for Hertz'

Found at: Muscle Car Blog News