Make your own, it is very easy.
Just take your favorite photo of your boat, use Photoshop or Corel PaintShopPro, or any other photo software, create a 4x6 photo along with your cute saying. Add some Christmas greenery and holly around the edge. Email it to Costco's website, done. Or, you can just create a template with the saying, and a empty space for the photo, then copy/paste different photos into that empty space. This way you can have a selection of different pictured christmas post cards.They are quite reasonable, and quick. Their normal 4x6 prints are only $.19 each. A 4x6 size is perfect for post card size, or stick in a envelope and mail it. Also, a postcard only need a $.23 stamp. Just write the people's names and address on the back of the photo, stick $.23 stamp on it, and off it goes.Many stores or photo processing places have their own Christmas templates, but they costs a bunch more. Just create your own.IMHO, it is the only way to go.