Here is the fan mail address for Marina & Gwendal:

Marina Anissina & Gwendal Peizerat
Federation Française des Sports de glace
35 rue Felicien David
75016 Paris
FRANCE

I've written them via this address (which is in fact the address of the French skating federation), and I can tell you that it works!

If you really want to get an answer, here are some tips (although I can't promise that you will get one, don't forget that Marina & Gwendal are very busy!):

• first of all, always write your address on the letter, and not just on the envelope, because envelopes are likely to get lost!
• you are more likely to get an answer if you join a self-addressed stamped envelope to your letter, so that they can use it to answer you (that's what I did!)
• don't just write "hello, my name is ... and I would like to receive an autographed photo from you, bye!". Show them how much you like their skating and give them some piece of advice, etc.
• don't be disappointed if you don't get an answer, because they surely don't have the time to answer to everybody.