The "Number 1" resource for Barbershop is probably at SPEBSQSA, the "Society for the Preservation and Encouragement of Barbershop Quartet Singing In America. (Other places have similar orgs.).

"Official" arrangements for a number of songs are at SPEBSQSA: Get Music You should be able to find sufficient samples to "analyse your own theory" of the style.

Since "real" Barbershop is NEVER accompanied by instrumental backup, it's virtually impossible to use "equal tempered" scales or harmony. Even if you write it down that way, unaccompanied singers will naturally revert to "harmonic scales," and the beauty of the style is that it's one of the few places one still gets to hear the "old way."

John