If you cough up the cash, there are G4 Clamshells to be had on Ebay, although I personally wouldn't buy one of the currently available ones for several reasons.
I'm trying to add one to my collection, but I will more than likely buy one in England and outsource the work to there
BTW, I'm generally in agreement. The Clamshell design is interesting(which is why I have several) but ultimately it's big, heavy and just generally as "un apple" as could be now.
Within my current field of view(aside from the computer I'm using) there is a 13" unibody(non-retina) MBP, a Clamshell, and a Portable. It's telling to me that the Portable and Clamshell are closer in size than the Clamshell and the 13"