This in no way a complete list. This is just royals we've written to, or have been asked to find the address for. If you are trying to find an address for a Royal Family not on this list, just ask.
Bhutan
Royal Secretariat,
Tashichho Dzong,
Thimphu, BHUTAN
Royal Secretariat,
Tashichho Dzong,
Thimphu, BHUTAN
Japan
The Imperial Household Agency
1-1 Chiyoda,
Chiyoda-ku, Tokyo, 100-8111
JAPAN
Jordan
Royal Hashemite Court
Amman, JORDAN
Lesotho
The Royal Palace Secretariat
P.O. Box 527
Maseru, LESOTHO
Thailand
The Grand Palace
Na Phra Lan Road
Bangkok 10200
THAILAND
For Princess Maha Chakri Sirindhorn:
HRH Princess Maha Chakri Sirindhorn's Personal Affairs Division
Chaipattana Building, Chitralada Villa, Rajvithee Road, Dusit District,
Bangkok 10303, THAILAND
Tonga
Palace Office
Halatu'i, Kolofo'ou,
Nuku'alofa, Tongatapu
TONGA