I heard that Bhagavad Gita is referred to as Hari Gita. I don't know the exact reference. Where is it referred as Hari Gita?
Hari gita is another term used for Bhagavad gita which is referred in the section CCCXLIX of Shanti Parva in Mahabharata. From Keshav Srinivasan's answer:
In the beginning of the Treta Yuga, Vivaswat imparted the knowledge of this cult to Manu. Manu, for the protection and support of all the worlds, then gave it to his son Ikshaku. 2 Promulgated by Ikshaku, that cult over-spreads the whole world. When the universal destruction comes, it will once more return to Narayana and be merged in Him. The religion which is followed and practised by the Yatis, has, O best of kings, been narrated to thee before this in the Hari Gita, with all its ordinances in brief.