No idea about the website, but we saw the stands for Santa letters when we were there last week. There is a stand in Studios - in front of cinemagique - and one waaaaaaaay in the back of Frontierland at
Disneyland park. We picked up the paper in Studios and dropped it off the next day in Frontierland. Then we found out that they don't send replies to the United States!!!!

Major boo! My daughter is 18months and I thought it would have been really neat for her to get a letter from Santa.
--Heather