When it comes to a player attempting to join a Kingdom, it seems to be extremely limited on what you can do. You can see the Kingdom name, requirements, and member count. Other than that, you get the ‘need an invite’ notification.
What you should add is a Kingdom Info. link within the screen. This will allow you to see more details about the Kingdom including the leader’s name (as well as a ‘Message Leader’ link). This way, it gets the players a chance to ask for an invite rather than just saying it in world chat over and over hoping for the best.