Mana Leech for elemental attack builds

First of all i love the game and for an EA ist realy good, just one think is atleast for me realy frustating. As an Elemantal Attack build u dont have some leech for mana and cant sustain enough for bosses in the endgame. Dont get me wrong i can kill all map Bosses to area lvl 82. But if u do Breachboss or so, my mana flask is not eneough to sustain the mana. Maybe we can get something like leech #% auf elemetal damage on gear/ jewel etc or a node in the passive tree around the ranger area