To download version 10.5.1, you should use official Broadcom channels to ensure you receive a legitimate and secure installer: Broadcom Support Portal

If your organization absolutely requires version 10.5.1 for legacy compatibility, there is only one safe route:

Once you have obtained the legitimate , follow this procedure carefully. A misstep can lock you out of your system.

Symantec (now Broadcom) does not provide a public "trial" download link for this software. Access is strictly controlled through authorized accounts: