I\'ve recently discovered, to my astonishment (having never really thought about it before), machine-sorting Japanese proper nouns is apparently not possible.
I work
For Data, dig Google's Japanese IME (Mozc) data files here.
There is lots of interesting data there, including IPA dictionaries.
Edit:
And you may also try Mecab, it can use IPA dictionary and can convert kanjis to katakana for most of the words
and there is ruby bindings for that too.
and here is somebody tested, ruby with mecab with tagger -Oyomi