You can still find the plugin (for versions 4.16-4.20) on the marketplace via your library tab in the Epic Games Launcher. However it has been deactivated so it doesn’t show up in a search anymore and you cannot add it to your library if you hadn’t already.
As mentioned the plugin is free and on GitHub, but you will need to link your Epic Games account to your GitHub account using the instructions at unrealengine.com/ue4-on-github since the repository is private. Otherwise you will see the following 404 error page:
This is due to the terms and conditions of the Unreal Engine EULA: “Any public Distribution (i.e., intended for Engine Licensees generally) which includes Engine Tools (including as modified by you under the License) must take place either through the Marketplace (e.g., for distributing a Product’s modding tool or editor to end users) or through a fork of Epic’s GitHub UnrealEngine Network (e.g., for distributing source code).”
Even though this specific plugin isn’t classified as “engine tools” we plan to distribute modding plugins in the future. Therefore if our plugins are no longer being distributed on the marketplace we will have the least restrictions by distributing within the private Epic Games network on GitHub.