Sorry for joining late, I would be disconnected for a while. You can read about najadum in captivity if you visit this site: http://reptilia.dk/
Not very encouraging indeed, and collaris must even be harder to maintain. One should also bear in mind that both species are threatened in many parts of their ranges. But of course both are also especially attractive, which makes understandable that they're sought after by devoted racer keepers.
Regards from France,
Benjamin.