I got my tickets for the Quarter Final in Cardiff in the post last week. I bought them through Ticketmaster months ago. I believe that they were released at different times during the last year and I got lucky. I also got tickets to the Ireland-Argentina and Ireland-Georgia but I had to pull a few favours for them. As far as I know the only way to get them now is through Tour Operators. By the way, for the Cardiff Game a Tour Operator might be your best bet as accomodation was very difficult to get.