Mahanarayana Upanishad is a part of ‘Taittiriya Aranyaka’ of the Yajurveda. It is the tenth chapter in the Holy Scripture.
Here you can download the PDF of Mahanarayana Upanishad for free.
The Atharvaveda also contains Mahanarayana Upanishad with the same content.
You are playing Seeksha valli instead of Mahanaryana Upanishd & calling it as Mahanaryana Upanishad