Robert Halmi, Sr., Chairman of the BoardAlternatively (or additionally) you can write to Peter Von Gal, Vice President, at the same street address.
Hallmark Entertainment Distribution Co.
1325 Avenue of the Americas
New York, NY 10019-6026
Simon Moore moved from London to Los Angeles, and so the old London address you might find on some sites is no longer valid for him. You can write to him now through the 10th Kingdom newsletter, as he has a column in it and answers fans' questions there (many fans ask the same questions).
10th Kingdom Newsletter
This letter was started by the administrators of the 10th Kingdom Connection message boards (the one currently in use by most fans), and subsequently given to Wendy of the 10th Kingdom Fan Club. You can subscribe to the newsletter here. It is not affiliated in any way with KingdomsPress, but is a publication of the fan club; however, as of this writing you do not need to join the fan club to subscribe.