There is more Pokémon merchandise than you can possibly imagine. Cuddly toys, clothing, key chains, tiny figures, build your own models, Pokémon monopoly, books etc etc etc.
DS2 has a tub of tiny Pokémon figures that he just adores. And also a Pokémon guide book (which lists hundreds of the things) that he peruses all the time. He loves little pokemon danglers that he attaches to his book bag at school.
The card game is pretty easy to learn (you can buy a starter set that teaches you the game). Some branches of Waterstones run children's Pokémon clubs where they can learn how to play and have matches against people their own age.
DS2 really likes making Hama bead Pokémon. You can google for loads of templates to follow and make little pixilated Pokémon. You need lots of different colours of beads (and tonnes of black) but DS2 loves doing this. I just print him off the picture and he makes loads of Pokémon.
He's also got a learn to draw Pokémon book that gets lots of use.
You can also download a free Pokémon tv app to watch episodes from the million series of the cartoon and also some of the hundreds of Pokémon movies.