You can go to the robot's web server and use the search tool. It is just a basic text search that looks through every program.
In looking how to find the search tool on the webserver, I actually stumbled upon a "Find and Replace" tool through the teach pendant. In OLPCPro, under the Teach tab, it has a find and replace window that shows you which program it is in and what line of code it resides. You can even limit which program you are searching.