You have a few options;
1) Make a copy of your source and change the auth port and game port for your second source.
2) Modify your auth server so that it is seperate from your game server and, then run 2 game servers with seperate soruces with different ports and have the auth server send the client to the different game servers.
3) Have your game servers lookup their ip and port from a database and have the auth server send the client to the correct game server (this is how i do mine), i can run as many game servers as i like using the same source and it grabs the correct port from the database, this reduces human error dramatically as the server will not start if the server is already running somewhere.
My auth server does no communicate with the game server either, it uses a little known client feature to determine which character to load.