Try http://www.karten-online.de/ or call the ticket hotline (Germany) 05 21 - 560 500 between 10 am - 6 pm (Mo.-Fr.).

If you want Stehplatz Innenraum tix for the Munich gig choose PK 2 for 69,15 Euro (see additional information at the bottom of the page).

By the way, I made the same experiences as the others. U2 gigs were totally sold out this summer but to prevent unfair prices at the black market or at ebay they released regularly tickets at eventim.de or getgo.de.