I’ve come across books and websites with monologues written just for auditions, NOT taken from a show.
Because I’m on the music side of music theatre, I’m not sure how often those free standing monologues are used, but I certainly wonder why there isn’t such a resource for songs (or why I haven’t come across them if they do exist).
Imagine, if songs were written with audition as their sole purpose, a 16 bar or a 32 bar wouldn’t be a cut. Each song would have an emotional arch and would show off the singer’s voice by having a climax right where it needs to be.
Picture from http://www.taltopia.com/s/audition-songs