A thread on another forum showing King Thibaw of Burma with a tulwar got me looking at pictures and paintings of Thai and Burmese royalty. I ended up finding these pictures of King Buddhayodfa the Great (Rama I) and King Buddhaloetla (Rama II). I don't want to read too much into a painting that I have no idea of the provenance of. It does not show them with traditional Darb or with what would be european blades. To me the hilts, which is all that is shown looks like some of the vietnamese sabers we see. It could be seeing what you want to see though so I am posting them here for your thoughts. I do wish it showed the entire sword. And one of the swords I think these hilts resemble can be found here on Artzi's site
http://www.oriental-arms.com/photos.php?id=2173