I would try to get a custom steel frame done as a exact clone of the Cervelo Superprodigy... since they don't make them anymore and I'm unsure about the idea of buying used frames.

If that was not possible, a Crumpton frame like the one below. This example weighs 1600g and is rather small. I ride a 58cm, so mine would probably be more like 1900. Still not impossible to build around 16.5 pounds....