Official BlackBerry servers are no longer active, but community-maintained archives like the BlackBerry 10 Autoloaders directory on Internet Archive host many of these files. Internet Archive for a certain OS version or help with a "Connecting to Bootrom" Working autoloader for BB10 STL100-2 10.3.3? - Facebook
Before you go through this effort, understand that as of early 2022. An Autoloader will give you a clean, snappy OS, but you will not get back the ecosystem. blackberry stl100-2 autoloader