I'm assuming you are referring to one of the tiny little screws that hold the secondary plates onto the shaft. I'm also assuming you missed the part in the how-to thread that advised how to avoid that problem. In that case it sucks to be you. Tough break, lad.
I dunno, can you pick the other screws up with a magnet? If so maybe you should get one of those magnetic retriever things they sell at auto parts stores. Some of them come with mirrors and lights on them. I don't think you want that screw to go through a cylinder though. Could be terminal.