I just purchased this by going to the Blizz store from my browser. You can also access the store form the desktop app but whenever I open up a webpage from there it freezes. In the pet section the Guardian Cub is sitting right there, with 'Learn More' below it. Clicking this takes you to your battlenet account where you will be able to complete the purchase for £9. Select your account, character and then log into the game. Mine arrived after a few minutes.