You cannot without cheats.You maybe be able to get it in the future by mystery gift.
You cannot catch Genesect on Pokemon Black or White. You will need to go to a Pokemon Event. No Genesect events are announced yet.
genesect can't evolve
Genesect was given away as a wi-fi gift for a month after White 2 and Black 2's release, either version could get it.
Genesect is a legendary Pokémon which means no NPC trainers will be holding one.
In order to get Genesect in Pokémon Black 2 and White 2, trading is required.
Wait for a wifi event
You can't without hacking.
Genesect is an unreleased Event Pokémon. It cannot be obtained legally. (yet)
There are Victini (Event), Virizion, Cobalion, Terrakion, Tornadus (From Pokemon Black), Thundurus, Landorus, Reshiram (From Pokemon Black), Zekrom, Kyurem, Meloetta (Event), Keldeo (Event), and Genesect (Event).
you use action replay dsi to catch genesect(genesekuto)
you cant you have to wait for the special distribution
its not possible in the 1st black and white but you can with cheats also you can in mystery gifts in the 2nd version for a limited time only