There are several in the market but, as far as I can tell, they are all more expensive than the one from The World Parrot Trust. Now, I don't like or donate to this organization because they have worked with places that use parrots for commerce and with very iffy records (like Loro Parque, for example) and support what they call 'responsible' breeding for parrots something, which, in my personal opinion, doesn't exist but I figured you should all decide on your own...
http://store.wptestore.com/2017-calendar/