/OA_MEDIA/ is a virtual directory and points to $OA_MEDIA path in the server.
If you have access to Oracle Application Server then take the following steps. Or simply ask your Application DBA to perform the following steps and give the directory path to you.
1. Open a new terminal session > login as 'applmgr'
2. Setup the application environment by running the application '.env' file.
3. Simply type echo $OA_MEDIA. The path returned is the virtual directory path of /OA_MEDIA/.
If you are on R12.2 or higher then the output will be something like this - /u01/oracle/VIS/fs1/EBSapps/comn/java/classes/oracle/apps/media. Where VIS is the context and fs1 is the live application environment base directory.