This might sound like a silly question.
I can't figure out how (if possible) to use brew on OSX to install an official branch of a GIT rep.
Is there something i'm missing?
Homebrew can only install software that someone has created a recipe for. It isn't a general-purpose installer.
If you know how to install the software in the Git repository, you may be able to create a Homebrew recipe to install it. If you don't know how to do that, though, Homebrew won't be able to help you.