I've used Viagogo.com for U2 tickets - it works like StubHub but sells internationally rather than just to North American users and was established by one of StubHub's original founders.
I used them for the impossible to get GAs for Coimbra 2 and have just used them again for GA for Montreal 2. Paid double for the Coimbra GAs (but well worth it to get to hear Boy Falls From the Sky!) and they arrived within a week of ordering. Got the Montreal 2 GA for just over face and the ticket arrived 2 days after ordering.