In United States, each state conducts its own bar exam. While in Japan, there is only one bar exam (Shihou Shiken), which is conducted by Japanese government (National Bar Examination Commission).
So, Japanese attorneys (Bengoshi) all have the same qualification and can handle all legal cases throughout Japan. For example, I am a member of Yokohama Bar Association (which is the bar association of Kanagawa prefecture), but I am able to handle the cases anywhere in Japan, from Hokkaido to Okinawa.
Of course it is better to consult an attorney in your own prefecture from the standpoint of travel expenses and time, but if you cannot find an attorney (lawyer) near you, don’t forget that you have an option to hire an attorney in different prefecture.