frank,
This is rather unusual. Normally Avast is prompt to reply. Have you tried to contact them via the support email?
If that fails, try sending a message to VLK who is our Senior Moderator on the board. Clicking on "VLK" should bring up your email client and you can try to contact him. He should be able to get in touch with the Avast team to get your registration key.
Sorry I can't give you one, but the one I have is assigned to my copy alone.
Good luck
