Who's the other Uchiha Danzo mentions while recruiting Torune into the foundation
Canon
No clue.  The episode Shino vs. Torune! is a filler episode during the 4th Great Ninja War. As such, there is no canonical information who the Uchiha member is.
Non-Canon; Speculation Only
It's possible the Uchiha member Danzō mention was actually Itachi. In the episode, Danzo says to Shino's father

As you know, The Foundation is where ANBU agents are developed

While The Foundation lead by Danzō, it is a subdivision of ANBU

In Konoha, there exists a special branch of the Anbu known as Root. It was created and led by Danzō Shimura

Itachi joined the ANBU at age eleven, and Torune looked roughly the same age when joining The Foundation. Despite Itachi being apart of ANBU, and not The Foundation, Danzō still had influence over ANBU memebers and their missions.

Itachi reported the mission's success to the Third Hokage. The Third, having been unaware of Itachi's assignment from Danzō, regretted to hear the news