Looking for a Darkrai, not really picky about it. Can offer:
Any of the starters.
Zorua.
Any of the White Forest Pokemon, save Seedot.
Any of the non-Legendary Pokemon not found in White/Black, save Nosepass.
fDW Pokemon: Dratini, Bagon, Vulpix, Abra, Gligar, Hoothoot, Makuhita, Mawile, Goldeen, Anorith, Lileep, Illumise, Miltank, Skarmory, Slugma, Shuppet, Spoink, Pachirisu
All freshly hatched, can infect with Pokerus if need be.