You actually can list files from your classpath using the code below:
InputStream stream = this.getClass().getClassLoader().getResourceAsStream("assets/enderstuffp");
BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
try {
while( reader.ready() ) {
System.out.println(reader.readLine());
}
} catch( IOException e ) {
e.printStackTrace();
}
where this represents your mod class and "assets/enderstuffp" is your assets folder
It prints a list into your console of all files and folders within the assets folder.
Please note that it doesn't do a "deep-search", so you need to write your own method for that if you desire to do a deep search.