You can find them at grocery stores anywhere in the month of December. There are all kinds of sizes and price, and the inside varries depending on what you choose. 
When I was a child, I LOVED them so much and I used to wear them to play around (even if I had only one boot!) until I lost the soles. I wonder who invented them but they obviously came from the idea of Christomas stockings.
Another custom I must mention is that Japanese eat "Christmas cakes" to celebrate Christmas.They are not anything like puddings or pies, but they are a whole cake beautifully decorated. I must get pictures of them sometime but fancy ones are so beautiful and expensive, and you need to order it in advance if you want to get one of those special ones. I always took it for granted but found out it was not the way to celebrate by the real Christians. For some reason, Japanese eat a cake for Jesus's birthday!
If you don't care for those fancy ones, you can always buy one of those in a box piled up at the front of the stores, and they go on sale at the end of the 25th. There used to be a way to describe women who didn't get married by the age of 25 - they were called "leftover Christmas cake". As more and more women choose to stay single even after 25 nowadays, this is not used any more, I hope! If not, I was a mold Christmas cake when I finally got married at the age of 30!
Here are some samples of fancy Christmas cakes!
People lined up to purchase a cake for the special day!
