I got mine by pre ordering on Amazon.com and cancelling. Not sure if it works anymore, and if it does I think it takes a few days. Best bet would be to post on reddit.com/r/teraonline asking if anyone has a spare key they could send you. Always a few floating about there.
Not for NA beta I'm afraid.
Sign up on their site for the beta list or buy the Digital key (like £5) for promised beta access.
Not for NA beta I'm afraid.