Paul,

A while back I obtained a copy of a publication from the Smithsonian Instution
titled: Accessible Exhibitions, Testing the Reality.  This has specific
information on exhibit cases and accessibility.  The snail mail address listed
inside is:
Institutional Studies
Smithsonian Institution
900 Jefferson Drive, S.W.
Washington D.C. 20560

I also contacted the Mid-Atlantic ADA Information Center and am currently
evaluating the information I received from them, but I don't think it will
have anything that is exhibit-specific.  However, if you were interested in
building ATMs...  Their number is: 800-949-4232

Hope that helps... let me know of any other sources you obtain.  Thanks.

Mark C. Vang
Freya Ventures
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2100 Mediterranean Ave. Suite 15
Virginia Beach, VA 23451
(804) 340-0099