When an item is in stock, you will be able to add to cart. When it's out of stock, it will display as "Sold Out" and unable to add to cart.

Please click the "Notify When Available" button below the "Sold Out" button and enter your email to get notified when the item is back in stock. Products on the official store flies off the shelf so trust me, enter your email and grab it as soon as you receive the notification.