The NPB put out a general call today for people interested in becoming NPB umpires. The requirements: 25 years or older; better than 1.0 vision (Japanese measurement); and 175cm or taller. People interested in a position will need to mail in their resumes. Those that make it past the initial screenings will then proceed to the next two steps: fillings out documents and then taking a couple of skill tests.
You can get all the information you need by clicking the link above.