Now in 2018 as macOS Mojave is released I would highly recommend you to install macOS Mojave on your mac because it contains many bug fixes, new features and also apfs file system is more stable as compared to macOS high sierra. But if your mac is not supported by macOS mojave then you can download macOS high sierra from these download links.
This article contains links which can be installed on a real mac as well as can be used to build a Hackintosh.
Download from the apple app store.
macOS high sierra can still be downloaded from the official app store, whenever Apple releases a new version of macOS they make the older version of macOS hidden but still they can be accessed and installed on a mac.
To download macOS high sierra from apple app store go to this link, it will automatically open the app store if you are opening the link on a mac.
Download from Apple’s server.
The download links present in this section are from Apple’s server directly. You can download every version of macOS from the apple server directly. However you will not get a single .app format from it, they are in dmg format and are multiple files and cannot be used directly to upgrade your system to macOS high sierra. But you can use these images to make a bootable USB from these images use can restore the images from disk utility into a USB drive and try to boot with it. A more detailed guide can be found in insanlymac.com but it is Hackintosh focused but it will also work on a real mac.
The direct download links for macOS high sierra 10.13.6 from Apple’s servers are:-
Download macOS high sierra dmg for Hackintosh.
This dmg image is converted from the macOS high sierra 10.13.6 app. It is only for building Hackintosh. The dmg already includes clover bootloader, so you can restore the image and install the OS on your pc. Here in hackintoshpro we have a much detailed guide on how to install macOS high sierra on pc.
While macOS Mojave is released macOS high sierra still can be download and installed from the app store. If you are looking for installing or upgrading to high sierra on a mac I highly recommend you to download the app from the Apple app store because it is the easiest method, but if in some case it you are not able to download the app from app store then try downloading the dmg files from the Apple’s servers directly and create a bootable USB from it and then install it on your mac.