I just turned level 24 today. I've had 5 or 6 legendary engrams and not a single one has been legendary. I've done a fair bit of farming and no luck from that. I got a legendary fusion rifle from a blue drop a while back-but I've not met many people at our level who's had a legendary drop at all! I was talking to a few guys earlier and we came to the conclusion that you're better off aiming to buy legendary's-get your vanguard levelled up by doing bounties, and stockpile vanguard marks from the strike playlist. Then buy them from your class vanguard. Hopefully while your doing that you'll pick up something useful!