Just got an email from Redbox today, with a coupon worth $10 off of Last Of Us from Amazon. Apparently I got it from renting (and beating) the game right after it came out. Looks like it has to be sold by Amazon directly, not third-parties. The code looks to be only one-time use, but if you rented it thru Redbox, you should be getting the same email soon.
My code is still available if anybody wants it. Code expires on 9/7/13.