Apple has released iTunes 12.6.3 with the App Store which can be installed alongside the latest version of iTunes.
Apple released this version specially for Volume Purchase Programs users who may need to use iTunes to install apps. However, you can get the App Store back if you install this.
If you've already installed a newer version of iTunes, you can download this version of iTunes on your Mac, PC 32-bit or PC 64-bit* and run the installer. After installation is complete, you can continue to deploy apps with iTunes.
Also, this "special" version of iTunes includes compatibility with iOS 11, iPhone 8, iPhone 8 Plus, and iPhone X and supports both Windows and Mac.