While the full OS is unavailable, Microsoft still hosts standalone Service Pack (SP) ISOs. These are
: This is a popular repository for legacy software. You can find various 64-bit editions, including Home Premium Verification Windows Vista 64 Bit Iso Download
Windows Vista Service Pack 1 All Language Standalone DVD ISO While the full OS is unavailable, Microsoft still
full installers but updates for an already installed version. While the full OS is unavailable
If you are looking for a Windows Vista 64-bit ISO, here are the safest current methods to obtain it: 1. Trusted Community Archives
Since official servers are down, community-preserved archives are the most common source. Internet Archive (Archive.org)