Send Variable.

Ok so lets suppose you have an integer with the number of players, Ill assume it's called playerCount.

Now, you need a MainCommunicator which will hold all the starting server and server waiting room code where you will do this, assign it a NetworkView component and in your script that holds playerCount add this.

 //If using Javascript
 (RPC)
 function SetPlayerCount(pC : int){
 
 playerCount = pC;
 
 }
 
 //If using C#
 [RPC]
 void SetPlayerCount(int pC){
 
 playerCount = pC;
 
 }

This is the function the server will be running on the clients, so in the server, each time playerCount changes you should run this code.

 networkView.RPC("SetPlayerCount", RPCMode.Others, playerCount);

Absolutely avoid calling this if the player is not a server, which can be done by

 if (Network.peerType == NetworkPeerType.Server){
 
 networkView.RPC("SetPlayerCount", RPCMode.Others, playerCount);
 
 }