There are two I can think of that could help you. Riccio Exhibit Services out of Charleston, Illinois is an excellent source. Also, Hilferty and Associates out of Amesville, Ohio at www.hilferty.com. Both have done outstanding jobs at sites throughout the Midwest and the country. Riccio worked for years at the Peabody at Harvard, and Gerry Hilferty's firm has created and designed exhibits for some of the most prestigious museums in the country. Hope that this helps.
Jim Sturgill
Executive Director, Athens County Historical Society and Museum