You might try pestering Remc, who created the Piccolo and Cell characters (and many others) at the 3D-CC. He's working on a Goku character right now, and has a preview picture up in the Comics section of his website. He has loads of DBZ pictures in his gallery here at Renderosity, also. It's worth the look. Here's a link to his website:
REMC's Third Eye Function

bruhah is working on a couple of the androids, but I don't know if he's planning to release them.

It seems that every couple of months, someone asks about DBZ characters. I think that other people have tried making Goku, Vegeta, and the others in the past, but never finished. I've thought about it, myself, but was rather daunted by the prospect of modelling Saiyan hair.

You might be interested to know that some fans of the series are working on DBZ mods for the computer games Half-Life, Quake 3, and Unreal Tournament.