[Police] money order and outlandos

Hey all. I have a ? about outlandos. I am finally going to sign up, but I need to know from all the US members how to go about paying them. How does one go about getting the international money order they refer to? The Post Office doesn't seem to handle money orders to the UK . Should I send cash? Any advice from anyone who sends funds from here to the UK would be appreciated. Thanks -Josh