A new EM12 based plug-in, the EM plug for Files and Directories, specifically designed to perform fine grained file and directory monitoring can be found in the Oracle Enterprise Manager Extensibility Exchange at:
Beyond your primary requirement of checking the availability of a specific file in a particular directory, it also extends EM in the following ways:
Which files have been modified recently in a specific directory?
What is the total size of files in a directory and subdirectories matching a regular expression?
Which log files have exceeded a size threshold?
How many new files are in a set of directories?
Which log files have changed?
How has a file changed over time?
What is the magnitude of change (file size, number of files, etc) since last data collection or over time (when using Warehousing)?