Where are .epub files stored in iOS?

I need to find where .epubs for iBooks are stored in iOS.

I have a lot of ebooks on my iPhone and iPad. I restored my MacBook last week and lost all the ebook files from iTunes. I haven't synced my (jailbroken) iPhone or iPad to iTunes yet, so the files are still on the devices.

I can root into the iPad through Netatalk or Cyberduck, but I can't find the actual location of the .epub files on the devices.

Does anyone know where I could find them?