Maybe it helps to look at the Soviet fighter pilot's (Lt. Col. Voskov, as portrayed by German actor Kai Wulff) suit version. Apart from the color, they should be identical. The white stuff under the collar could be velcro. I suspect you would not find that on a real suit, so maybe the suit was produced for the movie specifically. But that's only me guessing.
Looks like a movie version of a Russian GSh-9AP since the visor curves on two axes... but notice there is no retaining ring, so it would functionally be closer to a TK-4 (Chinese) the pressure suit itself is pure fiction.
see how this TK2 has no retaining ring.
Sorry for bombing this thread :-D
To be clear: he's right- I think it's an HGU 20. I'm pointing to Russian and Chinese equivalents which can be found for $200 or less and could be pretty easily modified to look more like the HGU. The TK-4 even has a red star printed on the forehead in many cases! Let me know if you need sources for these- cheers!