Go to the Killing Floor 1 Workshop here: https://steamcommunity.com/workshop/browse?appid=1250
Sign into your Steam account, subscribe to all the different mods you want to use on your server.
It won't automatically download the mods like new games do, for some reason... so you need to do the following...
Open the game, click "Multiplayer", then go back to the game's main menu.
You should see the mod being downloaded in the top right of the screen.
If it doesn't download all the mods, repeat the process, over and over.
Keep doing that until all the mods you're subscribed to have downloaded.
Navigate to where Killing Floor is installed on your PC.
Connect to your game server via FTP
Copy the Animations, Maps, StaticMeshes, System, Textures, Music and Sounds folders (and therefore the files within) from your Killing Floor installation on your PC to your server.
Click the "Fast Downloads Sync" button in your gamepanel.
That's it. Enjoy.