Latest Platform SDK includes MFC 4.2 source code!
I just installed the latest Platform SDK and noticed that it included source code for the CRT, ATL (with private use only license), and MFC 4.2.
There was no license agreement on the MFC source that I could find, only a "readme" that contained:
There are no libs, DLLs, or help for MFC - but there are make files to build them yourself.
These files have been included for reference purposes, in conjunction with the Class Library Reference manual and tutorial.
The Platform SDK claims that it will only install on Win2K and up. But you can build applications that will run on 95 and up.