I would highly suggest that you don't mess with the bootloader on your Mac unless you are in a position to format your machine.
Macs do not use grub to boot into OSX
The firmware’s built-in boot volume chooser (hold Option to activate
it) will recognize Linux boot CDs as well as bootable hard disks and
let you boot them. (They may be labeled “Windows”, though.) For
triple-booting you’ll get only one item in the built-in chooser, but
you can use GRUB, LILO, or NTLDR to act as a second-level menu to
choose between Windows and Linux.
A much better solution would be to spin up a VM in Virtualbox, and run
grub-mkrescue to create your grub recovery disk from there.
If you search a Mac package manager for grub software, you will find none: Likely because the tools have no use on Mac.
spuders-macbook-pro:Downloads spuder$ brew search grub
No formula found for "grub". Searching open pull requests...
spuders-macbook-pro:Downloads spuder$ brew search grub-mkrescue
No formula found for "grub-mkrescue". Searching open pull requests...
Attempt to compile from source
-Download grub source
Darwin spuders-macbook-pro.localhost 12.4.0 Darwin Kernel Version 12.4.0: Wed May 1 17:57:12 PDT 2013; root:xnu-2050.24.15~1/RELEASE_X86_64 x86_64
$ ruby -e "$(curl -fsSL https://raw.github.com/mxcl/homebrew/go)"
$ brew install bazaar
$ #The installation of bazaar pops up a warning that you need to export PYTHONPATH
$ export PYTHONPATH=/usr/local/lib/python2.7/site-packages:$PYTHONPATH
$ brew install autogen
$ cd /tmp
$ bzr branch http://bzr.savannah.gnu.org/r/grub/trunk/grub
$ cd /tmp/grub
configure: error: cannot find install-sh, install.sh, or shtool in build-aux "."/build-aux
It looks like the configure.ac was not setup for the Mac OS. If you are adept at compiling software, you may be able to modify it.
Your best bet will still be to install virtualbox, and create a linux VM and run the grub tools from there