Also (though perhaps closer to a privilege issue than a nepotism issue):
How did you find the teacher who helped you get ready for the audition?
How did you "pay" for the practice time to prepare for the audition?
Also networking, if you do gigs in the same region the orchestra is located you're bound to bump into a few of the members.
You can also just email the orchestra and ask when they hold auditions.
Also (though perhaps closer to a privilege issue than a nepotism issue):
How did you find the teacher who helped you get ready for the audition?
How did you "pay" for the practice time to prepare for the audition?