you can't.
No. Sinnoh is too new for a GBA game to come out
You have to migrate it from emerald, sapphire or ruby. (GBA)
If you want to fill your Sinnoh Dex, look on websites. There are lists of where to see every Sinnoh Pokemon. If you want to fill your National Dex, you have to import them from your GBA games.
Darkrai first appeared in the Sinnoh games. (Diamond, Pearl, and Platinum) It was never shown in the Hoenn games, so it is unobtainable in Pokemon Emerald, for it was not known then.
Yes!!!, its called migrating!!! you migrate only 6 a day in the pal park which is open when you complete sinnoh dex.
download a Pokemon gba ROM and no$gba
It depends on what ds game you are playing. once you get the national dex there is an area on each of the ds games (different between the sinnoh and unova games) where you can import pokemon from gba games such as emerald. YOU CANNOT TRADE NOR CAN YOU GET A POKEMON BACK FROM THE DS GAME
No, you cannot migrate GBA Pokemon to Pokemon Black/White.
To play Pokemon games on computer you have to download a emulator I would recommend these: Desmume No$gba (not for gba games) and for playing gba games: Visual Boy Advance
You can't. You can transfer Pokemon from your GBA games to Heart Gold, however.
no
No. The 3DS does not have a slot for GBA Cartridges and therefore cannot play GBA games.