Most screen savers are saved in the Windows/System 32 directory. So they have to still be there. They are all *.scr files.
If you have screensavers download from the internet they could be in other directory .You can search them just by writing the *.scr in the search box. When you find your screensaver you just right click it and select install. The screensaver tab should automatically open and see your screen saver in it.
Hope this helps!