I have been told that we can find promotional codes in physical copies of Catan. Is it true?
Right now you can get a code for a scroll in every Catan "The Rise of The Inkas" box sold around the globe. And there is a Special Edition of the board game in the Netherlands that includes a promotional code for the base game: https://www.999games.nl/de-kolonisten-van-catan-collector-s-editie.html
Apart from that, there are no promotional Codes available in board games right now.