In Nov. 1992 the Witte Museum in San Antonio opened an exhibit "Thundering Hooves:  Five Centuries of Horse Power in the American West."  Each of the four major exhibit areas featured a full-scale horse.  The current AAM director does not list a web site or e-mail address.  The ph. # is 210-357-1900 and fax is 210-357-1882.  I suggest you start with them.
Good luck,
Ruby