This is something I've wondered too. With all the 
CG anime that have been out for a while, where 
are all the sketches? Do they not get sold like 
the cels? Are they massively popular and all 
getting bought up in Japan? Are they massively 
UNpopular and no one cares enough to sell them? Or
possibly the studios are sitting on them for now?

I've been curious since I really haven't seen any 
from big-time popular series. . . Animebox has 
graciously fed my desire for Monster Rancher 
genga, but they seem to only have sketches from 
one or two episodes. Taro had some (expensive, 
IMHO) Angelic Layer genga, but then nothing more, 
although they updated a small number of Hikaru No 
Go sketches. But still unseen is anything from 
Hellsing, Dot Hack Sign, or quite a number of 
other "biggies". Curt at Asylum turned up a few 
Chobits layouts/rough sketches (which I wasn't 
fast enough to get the only one I wanted! Wah!) 
but I haven't really seen other dealers posting 
sketches from CG shows for sale.

I'm not a big sketch collector -- my primary 
collecting interest is still mainly cels -- but 
I'd be interested in *somethings* from Angelic 
Layer, Chobits, Hellsing, Dot Hack Sign, Witch 
Hunter Robin, etc. . . I'd also go after at least 
a few more really nice Monster Rancher things too.

Many Sharp Smiles,
--Drac (quiet lately due to family emergency)