As the OP of this thread, I apologize for never giving an update on my hunt.
It was a success. I found the real thing.
In late 2017 after a few calls with the gentleman who owned and operated United Pioneer, I was told that he was able to locate the one (1!)
very last example of the blue split-hood parka in a regular size, in their warehouse inventory. The model had been discontinued for several years and this one was sitting on a shelf. It was a Small, but it fit like a Medium (which is just by luck exactly my size). It was a 94B-L, which is the longer version of the regular 94B (if you trimmed the bottom, it would look the same).
When I got it in the mail, it was covered in dust from sitting for so long. But after a thorough dry cleaning, it was as good as new. The only difference between this one and the one on the show was A) the size, and B) the length. In every other way (color, material, pockets, buttons, hood, etc), it was identical to the model that Hopper wore. Like I said, the bottom of the parka would just have to be trimmed a few inches to match the one on the show.
I haven't used the jacket at all since I bought it, because I've never been able to find an accurate Hawkins Police patch (all of the ones I've seen online each have some sort of inaccuracy). I'm a stickler for details, so that's what has stopped me from putting the whole thing together. The American flag patch looks terrific, however, and was kindly provided to me by Dr Jones Sr.
And so it sits in my closet. Unless I come to the conclusion that nobody out there is going to make an accurate replica of the Hawkins Police patch, it'll probably continue sitting. Here are some photos:
Regarding the color: these photos look slightly different in hue on my iPhone and my older MacBook Pro. A lot of how the color shows up has to do with the lighting of the photos
and your display's calibration, and this goes double for the jacket on the show since everything is color-graded in post-production. In real life, this jacket looks navy blue.
Speaking of which...
BTW from the screen shots posted it looks like the S1 parka is Navy Blue and the S2 parka is Royal Blue. Is that just the difference between indoor and outdoor light?
I would be very surprised if they were different colors, or different parkas even. In my research (as far as I can remember anyway, since 2017 feels like several years ago), I don't recall seeing these United Pioneer parkas offered in two different variants of blue. My best guess is that it's just a result of the lighting.
Hope this helps!