Here is a trick I noticed the other day.
With you iPad connected to the computer and selected in iTunes, go to the Apps tab. Double click on an app in the app lis and it will automatically change the screen display (to the right of the list) to the page and folder the app is in.
You need to have been keeping your iPad synced with iTunes, of course.
Sorry, but other than that all I can recommend is a systematic search of your folders.