They used to be very hard to come by. I've had my account for a few months, and in late June they were selling on eBay for hundreds of dollars (don't believe me? Look for yourself). So, I got into the business of selling them. :-D

Now, though, they're less than a dollar and everyone seems to have invites out the arse. Nonetheless, it's still not public yet, so anyone who wants them still needs to have an invitation. That said, I've still got a load of 'em... just PM me.