If you are sufficiently motivated, NT 4 leaked many years ago and you could find it; it even has interesting things like DEC Alpha support & various subsystems still included IIRC. Perhaps you could find a newer version like 5.2 on GitHub or another site, but beware, as a Linux dev/contributor, you probably don't want to have access to that.

FWIW, I've stumbled upon both of those things in my personal research while I had legitimate access to the 5.2 sources as a student. It turns out Bing will link you directly to the Windows source code if you search for <arcane MASM directive here>.

Yes, I'm in the process of reporting this to Microsoft and cleansing myself of that poison apple.