I don't think the studio ever released many 
Kodomo no Omocha cels to the market.  They 
probably did release a small amount, or some 
artists stole some cels from the studio, then
sold them to the other dealers.  The situation is
kinda liked Pokemon, there're well over 100
episodes, but Pokemon cels are hard to find 
because the studio didn't release them to the
public.  The ones that're floating in the market
are the stolen cels from the studio.  When I
was in Japan a while back, I saw one guy sold a 
stack of Pokemon cels to Mandarake.  Those are
all grade A cels.