The best place to buy outdoor Christmas decorations is at your local hardware or home improvement store. They usually carry a wide variety of holiday decorations, including lights, wreaths, and inflatables. You can also find outdoor Christmas decorations online, such as at Amazon or Wayfair. If you're feeling creative, you could also make your own decorations using materials like foam board or cardboard. Whatever route you choose, have fun decorating and spreading the Christmas spirit!