Mirrors for Ubuntu, Debian, or Arch Linux are almost always organized as open indexes. This allows users to choose specific versions, architectures (x64, ARM), or desktop environments.
Stick to Linux ISOs, open-source utilities (Clonezilla, GParted, OBS Studio), boot CDs, and abandonware that has explicit redistribution rights.
Old FTP sites are still abundant with "work" ISOs. Try:
If you maintain an internal ISO library, always disable directory listing for /work/ folders, or password-protect them. If you are searching for a specific ISO, append -inurl:(htm|html|php) to your search to filter out modern sites and find the raw directories.