Many thanks to Lubomír Ondračka for his response and help.

On Mon, Jun 8, 2020 at 1:18 PM Brian Campbell <revolvingsound@gmail.com> wrote:
Dear Colleagues,

After extensive, yet unsuccessful, searching I am hoping the kalpavṛkṣa [which is this list] may entice someone to help me, or point me in the right direction, to access the following article:

Umesh, Mishra. "Physical Theory of Sound and its Origin in Indian Thought." AUSt 2, 1926, 229-290.

This article is referenced in both Harold Coward's Encyclopedia of Indian Philosophies Vol 5: Philosophy of the Grammarians pg. 537, and George Cardona's Pāṇini: A Survey of Research pg. 126.

With all best wishes,

Brian Campbell