Yes, the three lake pokemon (Uxie, Azelf, Mespirit) are no longer available. To obtain these pokemon you must send it over from Platinum, or receive it from a friend.

These are the only known methods currently. So please be patient while more updates come up!

Feel free to post, if you know of any more Sinnoh legendaries not available.

(Mew is also not available!)
(Either Palkia, Dialga, or Girantina Non Obtainable. You have the choiceto choose one of these (Palkia, Dialga, Girantina) pokemon. To get these you must either send them over from platinum or diamon, pearl.

The way to get these pokemon is by sending over the special Event Arceus that is being given out with the new Pokemon Movie!)