I have been working on to build a section on the Archaeology of Mardin (an important part of Tur Abdin region in Anatolia) for our Archaeology Department Library.
What kind of references were you looking for? Newcastle University where I work holds the Gertrude Bell Archive, from prior to the demise of the Ottoman Empire. Some of the images from her collection may include Mardin, though I think most of the material is about what is now Iraq and Palestine.
Also, I assume you must know Ömür Harmanşah? He's probably a good person to ask. He teaches at Brown. If you don't know his contact info, I can certainly send it to you. Best wishes, Zeynep