Same here, not much luck yet.
Some I found on the net that may be suitable are:
* DK-Digital DVD 367
* Scott DMX 10
* Umax "Chili" style 630x
NO clue as to whether these devices are any good to begin with, as they seem relatively cheap, and playing DVDs in a vertical position must be more tricky (i.e. expensive) than horizontal...
Good luck (and if you have found anything that works and is affordable, please let me know!)