Q. How can I find a full short story, The Furnished House by O.Henry, online through COM Library so I can cite it as my primary source?

The Library does have a print copy of The Complete Works of O. Henry by William Porter which does include The Furnished House, the call number to this 2 volume book is (PS 2649 P5 1953)

You are looking for an electronic version. Using guides, select the page, American Lit guide, Find Full Text Poems & Short Stories (link below).

Google Books is another source you can search, here is a direct link to The Furnished House by O. Henry : http://books.google.com/books?id=Fys-AAAAYAAJ&dq=o%20henry%20the%20furnished%20room&pg=PA239#v=onepage&q&f=false 

You can also download the e-book to your mobile device. Instructions on how to download are in the Google books guide (link below) on the Free Google eBooks page in the Download the Classics box.