Rare "Shree Bhargava-Tantra" is being cited in "Vaishnava PanchaRatra Agama Katipaya Paksha" by Dr. Ram Pyare Mishra in connection with BhutaShuddhi Mahatva:
I have added this Tantra in my future purchases list, because it is available on exoticindia (just 20 usd).
While scrolling via "Table of Contents" I have noticed that "Shree Bhargava-Tantra" has a separate Khanda, devoted to Shree Ashtakshara-Mantra!!!!!!!!!!!