Where is the best place to buy good quality house banners?

We are reading Harry Potter in my fifth grade class beginning in January, and I'd like to put up the house banners around the classroom, split up the students into houses, and have a friendly race for the house cup.

Any ideas where I can get good quality house banners? I've looked online but it's hard to tell which are most authentic-looking. (Perhaps that's a clue that it doesn't matter, though.)