It is highly unlikely that they just 'disappeared' .... so, they may have been moved. I believe iPhoto will display the file name of the photo when it shows you the preview. Are you able to see any kind of a preview of the missing photos? If so, can see the file name somewhere? If so... do a Spotlight search on a couple of the filenames. I don't know if you have to do something special to have Spotlight search for hidden files, but do a quick Google search ... those instructions are out there.
If you can't get the filenames as suggested above, then go back into Originals folder and figure out a few of the file names should be. Most cameras have some sort of prefix... like DSC and then tack on a serial number in sequence. So, just go to the last photo in the Originals and note the name. Then look for files that would have come after that photo.
Be sure not move, edit, or change any photos in the Originals folder though. That is what caused this mess in the first place. iPhoto is a database, and it needs the photos inside its library to stay there, and to stay untouched. The fact that you even knew the secret handshake to get into the package is not a good sign. Apple hides the contents on purpose to minimize the damage a user can do to the database. Not saying you did anything wrong, of course. Lets just try to find those images.
Luck