We got a Dutch door at Frank Lumber the Door Store. It's a little intimidating walking in but they're very helpful and not pushy about talking you into a sale. They have a ton of different doors and they will give you options. For a Dutch door they essentially take a whole door and cut and alter it into a Dutch Door. Ours turned out great.
I agree with Chris. Frank's Lumber is awesome and definitely worth checking out.
Thanks! Your answer is awaiting moderation.