In present-day India, such highest tantra can no longer be found. During the sarma or the New Translation period after Atisha (982–1054) had entered Tibet, some Tibetan translators arrived in India and realized that they could hardly find any Sanskrit texts on the Great Perfection. Even if they occasionally found one or two short paragraphs of sadhana in the private collection of some elder adepts, when they requested the elders for instructions, the elders would superficially answer, “This was collected by my predecessors. I know nothing about it.” Actually these elders were practicing in secret. They just didn't want to reveal anything.
[Excerpt from Luminous Wisdom Book Series ~ The Guru Yoga Practice of the Seven-Line Prayer to Padmasambhava]