I don't know what happened to all the emails with the codes either.
When I first bought my Kobo last year I was receiving codes every week or so. After a couple of months they stopped and so I signed up for Kobo's email list and the codes starting coming again.
However in the last month or so the emails are different. It's ages since they sent me a code. Last week I got an email about a book that I thought was interesting only to find out that it's not available in Australia!
So I also use GOAT's post to find current codes. I don't think I've ever bought a full priced book from Kobo - I always use the codes.