How to Find a MAC Address of Your Wiimote
This site lists some of the methods to get the bluetooth (MAC) address of your wiimote if you want to use the Manual discovery mode in WiimoteController. The Manual discovery can be found in the WiimoteController's preferences -> Connection Settings.
There are numerous ways of finding the bluetooth address of your wiimote. Some are listed on this site. If you know of another good and easy way on how to do this, you can contact me and describe the process (you can even make a tutorial like the ones on this site). I might feature you and your suggestion on this site.
These tutorials talk about putting your wiimote into discovery mode. This usually means pressing the One and Two buttons at the same time while the wiimote is off, so the lights on the controller start flashing and keep flashing for a longer time. If this doesn't work (sometimes a nearby Wii interferes with this process) use the red sync button under the battery cover.
When you do find your wiimote's MAC address, save it (not just in your android device) if you are ever going to need it later so you won't have to repeat this process again.
You should first try with the android app that I have made specifically for this purpose, called Bluetooth Address Finder. Just run the app, turn on bluetooth and begin the searching procedure. After the app says so, put your wiimote into discovery mode. The address will show up on the display. Tap it to copy it to clipboard. You can then paste it into WiimoteController directly by holding down the appropriate text box and selecting Paste.
While this should work on most devices, it might not work on yours, especially if the WiimoteController app doesn't usually find your wiimote. You can try this app with your friend's android device. The controller's MAC address is just as valid if another android device discovers it. In fact, you can use a computer to get the address too.
Here are some tutorials that use a PC. Bluetooth is of course needed in the PC to make this work. These tutorials cover Microsoft Windows XP's default bluetooth stack, a popular 3rd party bluetooth stack called IVT BlueSoleil and Linux with bluez. Here are the tutorials:
If you have another operating system or another type of computer, take a look at these tutorials anyway. Then find similar features with your setup. It's not hard at all. The general idea is to find your bluetooth configuration page, start the discovery process and put your wiimote into discovery mode. After the wiimote is found, try to learn its address by looking at context menus and sidebars for properties of the just discovered device.