Hey Chris305,
First let me say welcome to the forum. My name is radicalb21. There are two things you can do:

  1. SEND an email to support@avast.com . Then also give your name and the old email address you used and they should be able to find your old key.

and

  1. Go to the following url:

http://www.avast.com/i_kat_207.php?lang=ENG

I hope this helps. If you have any other questions please feel free to ask any and all questions