If you have the time and money available, the Honbu dojo of the Yoshinkan offers a senshusei course that will take you to instructor level in one year. Go to www.yoshinakn.net
for info. Tokyo is a beautiful city and the teachers are some of the best in the world. But then again, I'm prejudiced.
I have the time but not necessarily the money (I'll have ~$3500 to spend available at the end of my schooling)