[MENTION=464826]Duop[/MENTION]
Any carbon rim can be built up - Boyd, ENVE, HED, NOX, Reynolds, etc.
I had looked to have carbon rims + track hubs built locally. In the end I could not find a combination of carbon clincher with ceramic brake track + track hub which weighs <1400 grams and has the spoke count I wanted. If you are happy with 1600 grams and 24 spokes in the front with a track hub then you can build any number of combinations. Using a road hub with a quick release in the front will allow low spoke count.
But yeah, there are lots of carbon rims out there.
-Tim-