The 1930 census shows this family from Patton Twp., Allegheny County, PA:
John W. Calhoon 43, born in NC, first married at age 23 Rose M. 27, first married at age 22 Henry 4 11/12 John G. 2 3/12 Benjamin F. 2 3/12 Rose M. 10/12 All born in PA except John Sr. Rose's parents were born in Germany.
The marriage data would suggest Rose married John ca 1925. He was probably previously married. Your best bet would be to get their marriage record which most likely was recorded at the Allegheny County Register of Wills. It may have data on their parents.
You could also try to get Rose's death certificate which should have her parents' names and burial place if you don't know it. John is probably buried with her. The cemetery office may have some data and of course their tombstones would have exact dates or at least the years of birth and death. The PA Dept of Health would have her death certificate. I suggest getting a more exact date for John before tying to get his. Is it possible they are buried in McKeesport and Versailles Cemetery: http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GSln=calhoun&GSiman=1&GScid=2240007&GRid=33317193&http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GSln=calhoun&GSiman=1&GScid=2240007&GRid=33317193&
Their obituaries should prove quite helpful. I suggest trying the Western Pennsylvania Genealogical Society, Historical Society of Western Pennsylvania and if you know where in Westmoreland they died I can try to direct you to the appropriate library, etc to check with there.