Oh, nice. I didn't even know there was an official one (that's what you get for not using Twitter....)
I don't use Twitter either, but I found it while searching on Google. I really like the items and it's so nice that - compared to AC:NL - you can get them whenever you want and you don't have to connect to the internet.
Where exactly do we type these codes?
Go to the Post Office (it's to the right of the stairs that lead to the Castle in Castele) and talk to the Password Clerk (the Plushling on the right). Make sure to type the words correctly (meaning "Seasick sailors" and not e.g. "seasick sailors" or "Seasick Sailors".