My brother had one made as an interior door to separate the workroom from the showroom in his retail shop. He used the existing door, had it cut, hinges added and a small shelf put on top of the bottom door so he can lean on it and chat with customers. As an exterior door, depending on your climate, I imagine weatherstripping would be difficult if not impossible. The company linked below makes custom doors and that may be your best option.

Here is a link that might be useful: Lemieux Doors

both Simpson and Jeldwn have Dutch doors

both Simpson and Jeldwn have Dutch doors

Lemieux, Simpson, Jeldwen and many others all make the doors themselves but you will need a millwork supply house to have the unit put into a frame of prehung if you will. Dutch Doors while nice are as mentioned above about impossible to weatherstrip well and will be quite energy inefficient.