Most theatre auditions specifically do not want acapella auditions of any kind .. I would try to find a backing track that is not too intrusive .. without crazy background vocals, etc if you cannot get someone to accompany you.
I like this website: http://www.karaoke-version.com/customba ... horus+line
The reason I like it, is bvecause you can customize your track - mind you they do not have a uge selection, but they do happen to have A Chorus Line .. You can go in and take out background vocals, take out instruments, crazy percussion, etc. We have used it to nmake a very simple backing tracks to use.
best of luck!!!!