Apple's official support page still hosts a hidden link for "How to upgrade to macOS High Sierra" which redirects to the App Store, but you can use softwareupdate --fetch-full-installer --full-installer-version 10.13.6 in a Mojave or earlier terminal if you have the catalog URL. The "exclusive" copy is best sourced from a trusted Internet Archive user with a verified checksum.
The only safe sources are:
To ensure the software is free from tampering, it is strongly recommended to use Official Apple Support Apple Support Community Mac App Store (Full Installer): Compatible Macs can download the full installer via this App Store Link download+macos+high+sierra+10136+exclusive
If you already have High Sierra 10.13.0–10.13.5, skip the full installer. Get the (direct from Apple): Apple's official support page still hosts a hidden
To download macOS High Sierra 10.13.6, you can use official Apple support links or specialized third-party utilities if you are on a newer Mac that restricts older downloads. Get the (direct from Apple): To download macOS
Search for "Mist download" to find its GitHub releases page and download the DMG. Open Mist and navigate to the tab.