Great news! You know how lately I’ve been posting pictures of some items that are exclusive but not in the treasure book? I finally found out how to unlock them! I don’t know if it’s for all these items, but apparently certain Club Penguin memberships unlock certain items, such as the Speed Boat. Here’s a picture Dodgers4 snapped of the three month membership he purchased at Gamestop:
As you can see, in addition to gaining three months of membership with that card’s code, the Speed Boat item will also be added to your inventory. Neat!
Update: According to Nelsonbob101 you can get the Speed Boat, Hard Rock Guitar, or Bubblegum Cheerleader Outfit depending on which card you get. In addition, thanks to Safej16, I learnt that there are two codes – one for the membership and one for the item. There is a change the item code will also let you unlock an item from the treasure book.