Easy fix for missing download of macOS High Sierra, macOS Sierra & Mac Os X El Capitan in The New App Store in macOS Mojave.
macOS High Sierra https://itunes.apple.com/ca/app/macos-high-sierra/id1246284741?mt=12
macOS Sierra https://itunes.apple.com/us/app/macos-sierra/id1127487414?ls=1&mt=12
Mac OS X El Capitan https://itunes.apple.com/app/os-x-el-capitan/id1147835434?mt=12