The Transfer Authority for DOD for FY 2021 is located in the Consolidated Appropriations Act for FY 2021.  The OUSD Comptroller has a summary of Reprogramming Requirements for FY 2021 located at <https://comptroller.defense.gov/portals/45/documents/execution/reprogramming/reprogramming_overview.pdf>.  Every year you should be able to find this information the Defense Appropriations Act or the Consolidated Appropriations Act in the Section for the Department of Defense