PhysX vs. 3dsMax vs. DCC

I am totally confused about the version numbers. When you install 3dsmax they seem to use PhysX 2.8.5 (which does not exist officially). The latest 2.x version I know is
So here is my problem: I run my own PhysX plugins inside 3dsMax but from the time where they switched from 2.8.4 to 2.8.5 I cannot even initialize my engine anymore.
How can I compile my plugins against the Autodesk V2.8.5. version, when I do not have access to the LIBs and header files?
On the NVidia sites I cannot even locate the old versions anymore - luckily I backup them all.
Any ideas?