You can look at Duino-hacks/BoardListManager.py at master · WestfW/Duino-hacks · GitHub
It's in a rather unfinished state, but it's at last part way to what you're looking for. On a Mac, anyway. (It SHOULD be relatively machine-independent, except for knowing whether the boards.txt files live.)
(alas, it's also my first major Python program. So... be kind!)