Seventeen Ways to Find a Maiden Name
If within the past 100 years - death certificates.
If more than 100 years - all her children's death certificates.
Newspaper obituaries.
Her children's marriage certificates. (the application is probably a more likely source)
Public Church Libraries.
Unpublished records microfilmed at branch LDS libraries.
International Genealogical Index (IGI) on microfiche at LDS libraries.
Divorce papers from county courthouse where filed.
Newspaper indices by Anita Cheek Milner for records from burned-out courthouses and churches no longer in existence, bibliographies in book form, such as N.Y. Genealogy and Biographical (at Sutro).
Survey of American Genealogical Periodicals indices by Skip Perry; also state and local historical society quarterlies.
Look for wills.
Write local historical societies and ask for an index check.
Send out queries to periodicals and quarterlies in the areas where your ancestors were.
Deeds and other land records.
Sometimes a census will mention a mother-in-law.