The Fire offers don't get emailed, just applied to your account. Your only record of it is the DOC that comes to the Fire itself (and it's over on AmazonLocal). You should see the discount for this one during checkout (unlike the digital ones, where you just have to trust that it will work).
Same offer now on eInk Kindles, deadline to sign up is Oct 21 (these get emails). Complete your purchase no later than 11:59 p.m. (Pacific Time), October 28, 2012.