You can find digital editions (PDF/eBook) of Volume 3 through several sources: Free Archives

The Secret Doctrine Vol. 3 : Blavatsky, H. P. - Internet Archive

The "heat" surrounding this volume comes from claims by some Theosophists that Besant's version was heavily edited or altered. Some even argue it contains private "Esoteric Instructions" that were never meant for the public eye, leading to accusations that its publication was a violation of solemn pledges. Where to Find the PDF

In the vast, shadowy corridors of esoteric literature, few works command the reverence—and controversy—of Helena Petrovna Blavatsky’s magnum opus, The Secret Doctrine . For over a century, students of Theosophy, occultism, and comparative religion have pored over its first two volumes: Cosmogenesis and Anthropogenesis . But recently, a new digital ghost has been haunting search logs: .

: These form the basis of the cosmological and cosmogonical sections, presenting an ancient wisdom that predates written history.

You can find various digital and physical versions of Volume 3: The Secret Doctrine, vol. 3