There is no single window in Armed Forces where you can go to get Software requirements for Armed Forces. As far as Army is concerned, you can visit DDG IT and Army Software Development Centre, both at Rao Tula Ram Marg, New Delhi. But it is doubtful if you will be given any worthwhile information. Best way to track armed forces requirements of software is by keeping track of RFIs and RFPs which are issued from time to time on MoD portal.