This book is far more easily available than you might think. I don't know of a single jurisdiction (including Germany) where it's outlawed. Reprints and both commented and uncommented versions are readily available in many languages. This was the case even before the copyright had expired.

Once you get over the (nonexisting) thrill of having something forbidden and the novelty of reading a book written by one of the worst human beings in history, you'll quickly discover that it's meandering, confused, extremely poorly written and simply boring. Even most Nazis back then didn't actually read it.

If you want a more illuminating insight into the minds of the Nazi leadership, Goebbels' diaries are a much better read. These are far more coherent, better edited and generally easier to get into. Keep in mind however that Goebbels intended these to be published, so read them with a critical eye. Just like Mein Kampf, Goebbels' diaries are not illegal, but there are fewer complete translations available, if you don't speak German.