There are two ways to get your masterkey.bin (whether the 2nd way is illegal or not is, tbh, up to you):
1. Mod your Wii *somehow* (modchip? I can't confirm; sorry that I'm not much of a help here) and dump it to your computer. I don't have experience with this. You'd be better off asking for help at other forums.
or
2. Download it online. Note that this way is most likely illegal (in your country), especially if you help upload it to other people (and if you are getting yours through a torrent, that's pretty much automatic). If you just completely achieve it yourself, then as long as you have your own Wii, if the DMCA people come up to your door for *whatever* reason, you can say that you already own masterkey.bin and dumped it from your own Wii.
Also, if you ask me for masterkey.bin then I shall inflict torture to your life.