Where can I get a standalone nmake.exe?

I am pretty sure you can't. It's included with Visual Studio these days. You'll find it in the vc/bin subdirectory. Its only non-standard dependency is the DLL version of the CRT, like msvcrt90.dll for the nmake.exe version included with Visual Studio 2008.

The original download page and file are stored on Web Archive

http://web.archive.org/web/20120402130733/http://support.microsoft.com/kb/132084

There is opensource clone of nmake: https://wiki.qt.io/Jom#Download_the_binary_package