AFAIK Auto-Rx is only available mail order, online at the above link.
I have seen it touted around as a suggestion to use on different forums for all kinds of ailments, not from the producer. From my experience* what Auto Rx does, which is clean, it does very well and slowly. What it does not do is fix mechanical issues in your engine, make up for worn out sensors, fix injectors or things it cannot reach, compensate for under inflated tires, or an empty gas tank.
(*experience is with a single used bought '96 Honda C27A4 that had deposits in the valve area from too long OCI's and bad PCV valve, Also used in a very well maintaned F250 7.3L diesel and a very neglected McLane edger engine, results are depoits are greatly reduced in the valve area of the Honda as can bee seen by looking in PCV and oil fill holes and increased mpg by ~2mpg presumably by some cleaning of the rings and a decrease in darkening of the oil in equal number of miles with each subsequent OC. The 7.3 motor no change but not opened before or after and was used strictly as preventative measure so no change expected in operation, too many other variables to note any affect on mpg of fuel. )