I did some research on this "Yubari" ship. Yes, it was built between 1922 and 1923 as an experimental scout cruiser.
Link to Wikippedia:
http://en.wikipedia.org/wiki/Japanes...er_Y%C5%ABbari
Now, as for adding it, one would have to create a visual model to put into the game. And unless there's a model of the ship floating around on the internet, it may take a while to build. Then he/she would have to make certain files so the ship would sail properly; it wouldn't have to be dead-on realistic, but believable for a 4,000 light cruiser. And also some many other odds and ends that i wouldn't know what to start with.
You'll have to look around on subsim, I'm sure you'll find someone able to help you out (i can't because i don't know squat about modding, lol).
Oh, and dispense with the "Sirs," ya landlubber! Just call me Peggy!