Every message is equally likely when you attempt this kind of brute-force decryption with a one-time pad. The code you get is actually 100% unbreakable if the pad isn't intercepted.
The numbers station should be transmitting a message encoded with a one time pad. The one time pad itself should be physically given in person to the spies who you want to communicate with.
There are many variants on this, including pads which you hope your enemy will intercept.