Christmas cards project

We are thinking about starting a new project in the children's ministry at Northview. We want to have all the children write Christmas cards to soldiers. The only question I have is where online to get a TON of Christmas cards. I did a bit of Googleing and found a collection of Christmas cards at the Mixbook website but I would like to hear a review of their services before I choose them. Thanks for the advice. I just think it would be a good way for the kids to make a difference.