Yep, what Dan said, and there has indeed never been a lefty version.
They feature a very interesting 'tension-free neck' which is based around a steel rod where the nut and headstock are attached too, and a wooden outer shell that is not prone to the tension of the strings because the steel rod takes up all of it. It is ugly as hell though, as the headstocks on all USATK's I've seen don't fit very well.
The only lefthanded ATK's out there are the ATK300 (both Korean (trans amber and trans black) and Japanese (trans black only) made versions), ATK305 (Japanese made only, trans black only) and the PGB1 (Paul Gray signature, a fourstring tuned to B).
This is a USATK5. Note that all hardware and electronics are 100% identical to that of the Asian-made ATK's, and how the headstock is separated from the rest of the neck: