You can buy the pull chains for a few bucks at most stores such as walmart, hardware, and home cheapos. Drill a 1/4" hole in the light mounting hub and install the switch. Splice it into the black hot wire. I do this fairly often with new lights for closets, etc cause they don't come with pull chains anymore. Some will have a knockout for the pull chain. You can drill and mount them in florescent lights too. Make sure any string does not touch a light.