I don't have a specific suggestion, but maybe inquire with these people?

"The American Society for Theatre Research (ASTR) is a U.S.-based professional organization that fosters scholarship on worldwide theatre and performance, both historical and contemporary."

http://www.astr.org/about-astr

These people may also be useful:

"The American Theatre Archive Project (ATAP) supports theatre makers in archiving records of their work for the benefit of artists, scholars, patrons, and the public."

http://americantheatrearchiveproject.org/about

I found them through googling for the following: theater ephemeral archive

theater ephemera archive (Same search, minus the 'l') seems to yield a lot of UK resources, if that's something you're interested in.

Best of luck! :)