This problem comes and goes. Lots of people play the second level of Everest, so it runs out of codes every now and again. Don't worry, though. The codes should be back before too long.
EDIT: Oh, it seems I stand corrected. Sorry about that, I guess I'm not as up-to-date as I thought I was.
When I spoke to Vince at VMK (via phone), he told me that this feature would be going away. That was quite a few months ago. He said all you would get is a congratulatory screen.