Here are some websites with resources for monologues & scenes. These appear in no particular order.
Remember: when choosing a monologue for an audition (or several for college auditions) you need to choose one from a published play.
Theatrefolk
https://www.theatrefolk.com/free-resources
https://www.theatrefolk.com/blog/theatrefolks-top-10-plays-for-scene-work/
Beverly Hills Playhouse
http://www.bhplayhouse.com/Acting-Scenes-Database/
Theater Words
http://www.theaterwords.com/ten-minute-plays-and-scenes.html
Scenes for Teens full pdf of this book
http://www.mtgilead.k12.oh.us/userfiles/1083/Classes/20749/scenesforteens.pdf
LiveBinders Duets Monologues and Plays
http://www.livebinders.com/play/play?id=683242
http://www.livebinders.com/play/play?id=683242
Goshen College
http://libraryguides.goshen.edu/c.php?g=35796&p=227171
Free play script blog about theatre, acting, monologues, classroom lessons and drama improv games.
https://freedramaplays.blogspot.com/2014/09/free-published-duologues-play-scripts.html
This is a search engine at Stageagent—it might help you locate scenes with specific actors in mind.
Stagecripts UK
Playscripts
ProPlay
South San
https://www.southsanisd.net/Page/3594
Birdville High School Theatre
https://bhstheatre.wordpress.com/monologues/
The following are publishing companies who primarily require you to buy the script before reading it, however some may be changing that policy so you can check them out as well:
Samuel French
Dramatic Publishing
Dramatists Play Service
Stageplays
AUDITION PERSPECTIVES
Here are a few articles that offer some perspective about auditions. Some are referring to professional actors and their experience with rejection after auditions, some are about dealing with not being cast in high school plays or not getting "the" part you wanted.