GKS currently has 1 server for Gmod. It can be accessed at prop.gameknight.us
You will have to be invited for a password.
Despite being called “prop”, the server supports Prop Hunt, Murder, and TTT.
There is a workshop collection that the server will download for you upon connection, but you can download it ahead of time here.
You may need Counter Strike: Source for the assets and maps. You may also download these resources seperately: CS:S Resources