Here's a current list of places to download the Audition Client. The following are reference links for the Audition US Client if you want to save it to your hub of choice or if RB site downloads are temporarily inaccessible.
Official Redbana Direct Download: Includes raw ZIP file and link to Steam launcher and download. http://www.redbana.com/download.asp
Official Steam Download: For avid Steam Users that plan to play Audition on Steam Client.
You must be signed in and have Steam client before you can download : https://store.steampowered.com/app/349720/Audition_Online/
Google Drive Download: You have the option to also save this to your Google Drive so you have personal access to the installer (zip) file anywhere.http://bit.ly/AuditionGoogleDriveDownload
Media Fire Download : http://bit.ly/AuditionMediaFireDownload
*Updates : Dropbox download has been officially dropped. Steam update has been made on redbana site for downloads.