Go play in single player, fool around with a battleship... They have flak cannons, very nice ones at that., you'll see them for sale wherever battleship weapons are sold.
They certainly look brilliant and add a whole "epic" feeling to battles, for sure.
They give a sense of scale.
But, anways... I haven't really seen more than player battleships in combat on more than two occasions.
I don't really know how good they are.
So, yes, Freelancer has flak.
It's only for battleships, though - class ten turret.
I'm not sure how effective they are in PvP combat, though.