There are quite a number of resources using Library One Search. Use the search terms South Asia 1971. one interesting source is:
South Asia Crisis 1971 pubished by the U. S. State Depatment.
Another is !971 A Global History of the Creation of Bangladesh 2013 by Raghavan, Srinath
Look at the bibliographies in sources you find to discover other materials useful in your research.
Once again there are numerous sources using the search terms "Sexual Violence" War "South Asia". A good place to start is with the following article:
Armed Groups and Sexual Violence: When is Wartime Rape Rare though not completly focused on South Asia it is a good beginning source. Also look at:
Challenging Impunity on Sexual Violence in South Asia: Beginning a Discussion and Embodied violence [electronic resource] : communalising women's sexuality in South Asia / [edited by] Kumari Jayawardena, Malathi de Alwis.
These are just a few of the resources on this topic that can be found in the library or online.