Thank you, @ugnvs. I appreciate your taking the time to review and respond. I am very familiar with Synaptic, which is my preferred package manager.
However, that does not answer my question as to the source site containing the master tree for the specific Yaru components (Yaru-dark, Yaru-bark-dark) that I am looking for.
I am looking to replicate the activities, as outlined in this posting, for the Yaru-dark and Yaru-bark-dark themes.
Namely, I would like to download "source" and customize/build/install the revised themes.
I also want to be able to report/feed back what might be of use to others in the form of a change tar bundle, including patch files, as I have with the BlackMATE-border theme.