1) Do you have all files organised ( in German we have "verknuepft" or "verwaltet" by Aperture) or are your files on seperate HD's and you left the pictures where they are when you import your files?
Means, if the files are on their original destination (and are referenced) or stored in the library.
2) Seems, like you have the files stored in the library (otherwise you would not have to search for the files, right?)
3) If you "Rihgt Click" on the "Aperture Library" under: User/Pictures/Ap Library you can let "show package".
That's the way how to do on a German System. It might sound different on your system.
Inside this package you can look for the files inside the "vaults-folder", I guess. If not, you may find the files in the "Masters"-Folder. There is a manual under:http://manuals.info.apple.com/en_US/Aperture_3_User_Manual.pdf and on page 581 and the following
pages you might find something about "vaults".
Important: You should not move files from there to another place, but only copy it to another place.
Otherwise Aperture has no way to keep track of your files.
4) That's the reason I keep all files outside Aperture and only have them referenced to.
I rename all files first, and then move them to Ext HD's and keep on mostly by Export a new Ap-Library as a Aperture Back up. The files itself are backed up manually by myself.
Hope it helps