It seems absolutely unusual to me that a public institution like
a museum or a library will not grant access to their collection for
research.  It is simply against their principles.

From ICOM resolution: http://icom.museum/resolutions/eres65.html

  Considering that museums, as scientific institutions, are responsible
  not only for the collections which they house, but also for the
  documentation relative to these collections and to their field of
  research, which documentation should also be made available to
  research workers.

Gerhard Dangel
Augustinermuseum, Freiburg