Robert Hudson has C. parva listed as a regular on his site (Aqua Botanic).
Shawn Prescott has C. nuri and C. parva and C. usteriana on his site(FishVet.com). I think Robert H has C. usteriana, too.
Tom, if I had two C. nuri plants, I would send you one, but I only have one miserable little plant. At least it is not shaded now, and so I am giving it the best submersed conditions I can.
Some others to add to the wish list:
C. keei----said to grow well submersed. Looks like C. bullata with orange-brown color to the leaves in good light. Much easier to grow than bullata.
C. hudroi----Like usteriana, but shorter? Said to be another good aquarium plant.
C. yujii----Said by Jan Bastmeijer to be easy to grow. I don't know whether or not this includes submersed growth. Has a spectacular white flower with a purple spot on the throat.