When you type /fs_homepath in the Tremulous console it will give you an output, a path to a location in your computer. Copy that location and add /base to the end of it, then go there.
For instance on Windows Trem would give me the location "C:/Program Files/Tremulous", so then I add /base to the end of that: "C:/Program Files/Tremulous/base", and I go to that location. Now use this same method for your Mac.