Having just done this, I can say that Bayern tickets are extremely hard to get through the club, they sell out almost immediately. You can keep your eye on the official ticketing and try to order them as soon as they go on sale, typically a month or so before the game you want to go to. However when I did this all the tickets were gone within 5 minutes, and that was for the Energie Cottbus game! So I had to go through a broker which was really expensive, but I got what I paid for, I was literally right behind the goal in the nordkurve. The website I used was
www.getmein.com, it's an English website and other than the huge price markup the service was great, as opposed to automated confirmation emails and whatnot it was actual people checking in to make sure I got the tickets. Hope this long-winded response was helpful, good luck!