600s were definitely available in the US.
Not only do I have one, but I bought my original one from Tenex in 1993.
At the time, it was $179 for the 600, and another $110 for the 85MB HD option and $40 for an extra 1MB of CHIP. To receive an entire multitasking computer that had full color and sound, and a hard drive to boot, for around $300 was an insanely good deal. My friends were still dishing out insane amounts of cash for 386s.
Putz Electronics in Sacramento also had them, for $399 (list price) which was a joke.