No the William A. Blakley Library does not have a collection of sheet music. Some repoductions of portions of musical scores may be found in books.
You might try www.worldcat.org (a public & free database): go to advanced search, 1) either select the format (near bottom of screen) and enter a subject in the search box in the upper portion of the screen, and click search, or 2) enter vocal score as subject and in the next search box enter a subject, such as Oklahoma, and see what libraries have a particular piece(s) of interest to you. There is the option of going a library in the metroplex or requesting the item through Interlibrary Loan (ILL). If you need the latter, go to the library where you are a current registered card holder, to request and receive and return ILL material.
