It's a cg anime, so other than sketches I doubt you will be able 
to find cels for it ^^ There are a few cels out there but they 
appear to be very early designs (short Kaiba with green hair), 
and may not have been used in the anime... or I should say, I 
haven't met anyone who was absolutely sure about what the cels 
were used in. 

If you're looking for Yu-Gi-Oh sketches, many 
stores carry them (e.g. Anime Museum, Anime Game, Anime Chaos 
etc)

Hope this helps,

-Tenzink