Posting with Bjorn’s permission-
To answer your question:
There is the standard Juniperus procumbens, which grows in the higher elevation mountains of Japan, including in the Japanese Alps. This species tends to produce very hard deadwood and interesting twisted trunklines. The foliage on this species is somewhat coarse and does not (to my knowledge) produce scale-like foliage (although that's not to say it's an impossibility).
What you find more commonly in the US is Juniperus procumbens 'nana' which is the dwarf version of the standard procumbens in Japan. This cultivar has more compact foliage and can potentially produce scale-like foliage given certain environmental conditions. So for example, it is less likely to produce scale-like foliage in the hot humid temps of TN, but much more likely to produce that foliage in the cooler environment of the Bay Area in San Francisco. Older examples of 'nana' also seem more likely to produce scale foliage than younger examples.
With all that said, though, it is unlikely that a procumbens 'nana' will produce 100% scale foliage across the entire tree. More often than not, you'll find a mix of juvenile and scale foliage on any given plant.