Can't locate App Store in iTunes for macOS
Please check that the iTunes Store is not disabled in the Restrictions pane in iTunes preferences (see screenshot below).



App Store functionality has been removed in iTunes 12.7 and later.

Apple provides a version of iTunes which still contains the App section and App Store.
Please see https://support.apple.com/en-us/HT208079 for more info and download link.

This version (12.6.5) can be installed even if a newer version of iTunes exists on your machine (it replaces the newer version). It also stops iTunes from updating (e.g. after installing, iTunes stays at v12.6.5).
It does not work in macOS 10.14 Mojave, though.