I am in a particular situation. I have a MacBook Pro with no internal CD drive and both MacOS X (minimal setup) and Linux (my main system) is installed. During a cross-upgrade to Ubuntu 12.04 I messed up grub, so that my /boot/grub directory is basically empty. This means I can't boot Linux on the laptop anymore but only get into grub rescue.
Normally this is no issue as you'd just boot from a rescue CD or USB stick, but unfortunately with a MacBook Pro this is not possible (I have reFIT installed and it attempts to boot, but it fails and the manual says that Apple's EFI firmware is not able to handle this situation).
From MacOS X, however, I still have write access to the Linux partition. I've now been trying to figure out how to populate the /boot/grub folder with the necessary files, to no avail so far. The ISO image of Ubuntu 12.04 contains an EFI folder which is not what I am looking for, instead I need the normal.mod files for the grub version of Ubuntu 12.04. I do not have any other machine to set up a virtual machine of Ubuntu 12.04 to extract this from after a grub-install, so I am asking for ideas here how to solve this mess.
P.S.: I installed the Linux previously when I still had a working internal CD drive. This is gone now.