Buy the material from eris morn at the tower?

Probably the fastest way lvl up is to go to "The Dark Beyond" mission on the moon with heroic mod cranked up. Once you get to the the hive entrance kill all the thrawl that come pouring out then let the knight kill you or jump to orbit, then respawn and repeat. Still grinding for mine but this is how my friends are doing it, needless to say its a choice spot for lots of hive related bounties etc.