I was having the same issue – hadn’t played in 5+ months. Looked everywhere for the email from Guildwars2. Then had an idea and I did the pre-purchase from GameStop, was able to find my code in the GameStop app. If you did a pre-purchase, check anything you use like GameStop or Steam as it might be in your pre-purchase link from them.
For what it is worth (directed to ArenaNet) this is totally annoying. One of the things we (gamers) hate most and always seems to get misplaced and why I use sites like GameStop now. Cannot stand a misplaced CD key (can always find the CD years later and not the stupid key). Blizzard finally has it right and your codes are stores on your account (which you don’t need a code to enter). You get nothing from this for an online game because the server can detect multiple uses of one code. You’re just frustrating your customers. Believe me… if I couldn’t have found my code I would have just dumped the game forever.