A Game-Service-Provider (GSP) is a Hosting provider for game servers, that partnered with the WS Staff and Sa-Matra to provide hosting a game server with the King of the Hill by Sa-Matra mission. It allows Communities and individuals, who are not affiliated with the the WS Staff or Sa-Matra to provide a King of the Hill server with limited abilities to change configuration and build their own communities around it.
Currently, there's only one GSP available, which is GamingDeluxe. Buying a server will automatically include the price for the server and support itself, as well as a fee to be whitelisted to the database grid of King of the Hill (where players statistics and progress is saved).
There's more information available in the discord server of King of the Hill & Wasteland about renting a server, especially what can and can not be changed when renting a server.
There's no other way of hosting or renting the King of the Hill by Sa-Matra mission. Especially there is no way to get hands on the mission files needed in order to host a server on another dedicated own hardware.