I thought you might find this address helpful in your ongoing Kutner research:

Ann Hyde
Curator of Manuscripts
Department of Special Collections
Kenneth Spencer Research Library
University of Kansas Libraries
Lawrence, KS 66045

Apparently, this place serves as a repository of SF books, papers, etc. and is available to the general public. They almost certainly have some rare Kutner manuscripts, letters, and God knows what else.

Bon Apetite!