From the Aikikai website:
For those who are living abroad and wish to train at Hombu Dojo:
Anyone who is a member of the Aikikai Foundation can train at Hombu Dojo. Information below are frequently requested regarding this.
In order to train at Hombu Dojo you must become a member of the Aikikai Foundation. At dojo located abroad, this is usually done upon joining the dojo, or else upon registration of shodan grading. Upon completing registration with the Aikikai, you will receive a membership card and a membership number. These do not expire and are good for life. Also, upon registering shodan you will also receive an International Yudansha Book. When wanting to train at Hombu Dojo, please bring something with your registration number with you. For those who are not yet Aikikai members, please complete the registration at the front desk upon arrival at Hombu Dojo.
If you wish to train as a Visitor, you can participate in any Regular or Beginner class. Other types of classes are not available to you. It is possible to join as many classes of those two types in a day as you wish. The fee for training is as listed on relevant page of this website. Visitor fee, 1,575JPY/day is applied for those who train a few days. Please pay the monthly fee for more trainning. The monthly fee begins the day you pay it and ends at the completion of the calendar month, not 30 days from when you pay. Please be aware of this fact. You can begin training immediately after paying the fee if you wish.
Please take you uniform home with you each day. Uniforms can be purchased at the front desk, though any white martial arts uniform is generally acceptable. Hakama are worn by men from shodan and women from 3rd kyu. This is the custom at Hombu Dojo. However, if you wish, you can wear a hakama from the time you register.
All necessary requirements for entering Japan (Visa, lodging) are the sole responsibility of the individual. Hombu Dojo does not provide lodging, laundry facilities or any other accommodations.
It is possible to watch Regular or Beginner's classes at any time. Please arrive before the beginning of class and sign in at the front desk. As you enter the dojo, perform a bow from seiza just inside the doorway. If you are not training, please sit in the back of the dojo to watch and do not interfere with the participants. Please refrain from taking photos or videos.
AIKIKAI FOUNDATION Aikido World Headquarters
17-18 Wakamatsu Cho, Shinjuku-ku, Tokyo, 162-0056 Japan
Phone: (+81) 3-3203-9236, Fax: (+81) 3-3204-8145