Because CSR (now part of Qualcomm) no longer distributes this software directly to consumers, users typically find it through third-party repositories or vendor-provided links: Third-Party Drivers : Sites like TousLesDrivers host the official WHQL-certified version 2.1.63.0. Community Archives : It is also available on Archive.org
Official download links from CSR are no longer available, as the company was acquired by Qualcomm and the software has reached end-of-life status. However, the installer remains available through several legitimate archival sources: Csr Harmony Wireless Software Stack 2.1.63.0 Download 15