are all christmas tree shops closing

Not all, but many of them are. As more and more people are looking for alternatives to real trees, many shops that once sold live trees are now selling artificial ones instead. That being said, there are still many shops that specialize in live trees, and they may have special sales or promotions during the holiday season. You should be able to find a tree shop that's still open, even if you have to look a little harder than you would have in the past.