So, I was browsing eBay and saw advertised a Kato Amtrak 4+4+4 Electric Locomotive... For all I'd known Amtrak America had never had any such an engine and therefore clicked the item to investigate... In front of me appeared (what looked like) an EF81 in Amtrak livery!
It seems that, back in the day, Kato didn't want to put money in to actually designing the models for America and therefore just repainted a (very slightly) remodeled EF81. Of course, it could be an exact copy of another Japanese electric locomotive, but I haven't had the time yet to do further research.
Toni Babelony of the JNS Forum posted a message in the thread I created on this locomotive that indicated that this is much closer to a Seibu E851. Thanks for pointing this out! Here is the Kato page on the Seibu E851. You'll notice that the Seibu has port holes, and other differences, but is obviously what Kato used as a base for this Amtrak locomotive.
Meanwhile, here are some photos I've taken of EF81s in Japan:
And, of course, if this locomotive really does exist, then please comment and tell me!