I would create a script that clones (or pulls if already cloned) all your apps, then do a text search across all the directories.
The script maintenance is just adding one line per app.
Or you could use the links shown here to search directly in the server without cloning, but it would require the creation of an app more complex than that simple script and would need to hit the server every time you do a search.
Or an hybrid, using the link to get the list of apps to clone and create the cloning script for you.