To get Hanabi first you have to go to the old peddler and buy everything in the stock. then you go find her only at the leaf center. And if she is not their then talk to anyone like Hinata,lee,Tenten,ino,choji,ect. when you do when you talk to them it will say do you want to give this thing to hinata and pick yes.Then Hinata will say thanks and stuff. Then you go to that dumpling place and you will see hinata. (the dumpling place is at the leaf center.) Hinata well tell you if you want to eat with her and it will be like a 'date' when you finish you have to do it again so you have to talk to her again. so when your finish with your second date try to find hanabi. If she is not their then find someone else to hang out or 'date'. When you find Hanabi you have to 'date' her twice to unlock her.
(Answer from Tony on Yahoo Answers)