Several archival sites host ESXi 5.5 ISOs. These are not recommended for production or security-sensitive labs.
Warning: Third-party ISOs may contain rootkits, backdoors, or modified VIBs (ESXi packages). Always verify the ISO against VMware’s published SHA-1 or MD5 checksums if you obtain from non-official sources. vmware esxi 5.5 iso download
Running an unpatched hypervisor is like leaving your server room door wide open in a high-crime neighborhood. Several archival sites host ESXi 5
While outdated, there are specific use cases: Warning: Third-party ISOs may contain rootkits