The University of Wisconsin has Nash's collected works, including multiple drafts of manuscripts demonstrating the evolution of many projects through completion.
For and online summary of what's available at the University of Wisconsin now, go to: http://arcat.library.wisc.edu/cgi-bin/Pwebrecon.cgi?BBID=852
For help from a librarian there, go to: http://www.library.wisc.edu/ask/