Looking for screws? This is a place to start:
http://www.ifixit.com/MacBook-Parts/MacBook-Pro-15-Inch-Screw-Set/IF185-027
Do you actually unscrew the thing all the way out?
If you're looking for the screws.
http://www.welovemacs.com/9228148.html
How the HELL did you manage to lose a screw? Do you actually unscrew the thing all the way out? Anyways, go to the Apple Retail store and say that you lost the hard drive mounting screws on the Macbook Pro. Be sure to include whether or not the computer is the new unibody or the older version, and what size the computer is.