I don't know what kind of requirements you need to meet for your research project but you have certainly picked not the easiest subject both in terms of scholarship as well as in terms of generally studying it.

As for the following recommendations I am going to make: Know that my knowledge of the subject arises mainly from doing some on the side reading and research I did specifically so I could finally come up with a good answer on the subject here on Askhistorians. My focus is also Nazi Germany and not Imperial Japan and I neither speak Japanese nor Chinese, making assessing the scholarship that exists in these languages a pretty impossible task. Also, as a general word of advise, it might serve you better turning to your supervisor/professor for further guidance than to an internet forum.

That out of the way, here it goes:

If you have Harris, Port, Gols, Barenblatt, Wallace and Williams, you have – to my knowledge – the English language historiography on the subject covered. The topic is not exactly unknown but still somewhat understudied since – and this is a point a couple of reviewers of the works of Harris and Wallace&William have brought up –, the English language historiography suffers from a lack of utilization of Chinese sources. Tien-wei Wu, in his Preliminary Review of Studies on Unit 731 in the US specifically mentions this and points out that there is a collection of Chinese sources, entitled Selected Archival Meterials of Japanese Imperialist Aggression against China: Biological Warfare and Poison Gas Warfare (Beijing: Chunghua Book Company, 1989) that contains testimony by both members of the unit as well as people affected by their work. What I have not been able to ascertain is if this was indeed published in English since Worldcat does not seem to return any hits to me under that title.

What also seems worth looking into for such a project next to the secondary literature is the primary sources available to you in the US. The National Archives do hold sources collected and obtained by the US from both the occupation of Japan and their collaboration with certain individuals that were part of Unit 731. The War Crimes Intragency Working Group has published a report on declassified material in US archives, which you can read here and also a more longform introductory essay Researching Japanese War Crimes Records that even details research starting points in one of the articles contained.

Next to this, there is also the possibility of looking into the post-war trials dealing with Japanese War Crimes related to Unit 731. While it is fairly known that some members were excluded from prosecution in order to gain their collaboration with the US, there is still the possibility of looking into the understudied aspects of the Tokyo International Military Tribunal, which in contrast to its equivalent in Nuremberg is seriously understudied. Even more specifically concerning the crimes of Unit 731 and also even less studied – though Harris makes mention of it in his book briefly – are the 1949 Khabarovsk War Crime Trials of the Soviet Union against members of Unit 731 for preparing to use biological weapons. The materials concerning this trial have been published in both German and English as either Prozeßmaterialien in der Strafsache gegen ehemalige Angehörige der japanischen Armee wegen Vorbereitung und Anwendung der Bakterienwaffe. (Moscow 1950) or Materials on the Trial of Former Servicemen of the Japanese Army Charged with Manufacturing and Employing Bacteriological Weapons. (Moscow 1950). (I have put the worldcat link in there for ease of finding it in a library).

There is also more of a discussion of the above (if you prefer secondary sources) in Jing Bao Nie, Nanyan Guo, Mark Selden, Arthur Kleinman (ed.): Japan's Wartime Medical Atrocities: Comparative Inquiries in Science, History, and Ethics, 2009 and Till Bärnighausen: Medizinische Humanexperimente der japanischen Truppen für biologische Kriegsführung in China 1932-1945, Berlin 2002, both of which books that I'd add to your list.

And that about covers it to my knowledge. Again, I have no idea what kind of requirements are necessary for your research project but from what I have gleaned of the subject in my brief research of it for the purpose of finally writing a good answer on the subject for this forum, a standard work, so to speak, is still outstanding in English-language historiography because it would need to make use of sources in Japanese, Chinese, and Russian next to English and would also entail some archival research in both Japan and China that would require both language as well as practical knowledge of the archival situations in these countries.

Edited to add: It might also be worth checking out Wolfgang Uwe Eckart: Man, Medicine, and the State: The Human Body as an Object of Government Sponsored Medical Research in the 20th Century, 2006 for a more comparative perspective.