The Pokémon franchise as a whole is in one hell of a licensing mess. A year or two ago I did ask Jerome about it, but he stated that the rights simply aren't available. With the company focusing a lot on iTunes and Netflix now - even forgoing a Pokémon Origins home video release in North America (currently, Australia is the only country outside of Japan with one). The TV series and movies are still released in America on DVD via Viz Media, but in the UK...it's complicated:
Streaming:
Netflix:
Pokémon Indigo League (Season 1)
Pokémon Black & White (Season 14)
Pokémon The Movie: Black - Victini & Reshiram / White - Victini & Reshiram (Movies 14)
Pokémon The Movie: Kyurem & The Sword of Justice (Movie 15)
Nintendo Zone*:
Pokémon Diamond & Pearl: Battle Dimension (Season 11)
*Nintendo Zone is basically, if you're in a public place that's a supported Nintendo Zone hotspot, you can watch episodes on your Nintendo 3DS.
Download to Own:
iTunes:
Pokémon 3: Spell of the Unown (Movie 3)
Pokémon Origins (Special Series)
Pokémon The Series: XY (Season 17)
Home Video:
Studio Canal:
Pokémon 4Ever (Movie 4) -> Available on Blu-Ray
Pokémon Heroes (Movie 5) -> Available on Blu-Ray
Pokémon the Movie: Destiny Deoxys (Movie 7)
Paramount Home Entertainment:
Pokémon the Movie: Jirachi Wish Maker (Movie 6)
Universal Studios Home Entertainment:
Pokémon the Movie: The Rise of Darkrai (Movie 10)
Pokémon the Movie: Giratina and the Sky Warrior (Movie 11)
Pokémon the Movie: Arceus and the Jewel of Life (Movie 12)
Pokémon the Movie: Zoroark - Master of Illusion (Movie 13)
Pokémon The Movie: Black - Victini & Reshiram / White - Victini & Reshiram (Movies 14)
Pokémon The Movie: Kyurem & The Sword of Justice (Movie 15)
The original series was originally released on VHS by Warner, while they also had the theatrical, VHS and DVD rights to the third three movies, but they're all out of print, as is Contender Entertainment Group's DVD release of the Pokémon Chronicles special series.
So yeah, the rights are basically spread out absolutely everywhere. Notably, we are currently only missing movies 1-3 and 8-9 at the moment (movie 1 received a nice HD remaster in Japan last year, I'd like to see that). In regards to the TV series though...we're missing a lot, with none of it on home video and the ones that are available digitally, are scattered everywhere.
TPCi also have the entirety of the series constantly rotated on the Pokémon TV Android/iOS app. They only have a selection of each series for a week before they remove them and replace them with the next batch of episodes, which rotates.
Personally, I think a good idea would be for the service to be streamlined and for episodes/movies to be made available to purchase and download on the Nintendo eShop for 3DS and Wii U (SD on 3DS, HD on Wii U). I mean, Pokémon is one of Nintendo's top selling intellectual properties, so why the heck are they letting me watch Pokémon legally on my PS3, XBox 360 or on smartphone devices, which are constantly being blamed for reducing their sales?
Most people who like Pokémon will y'know, already own a 3DS and maybe even a Wii U, so would there really be anything to lose?