Cels Forum

About your question of "how long will the studio release
the cels", well, different studios have different policies,
there is simply no definite answer for it.
For example, it may take Toei (Sailor Moon, DBZ, Marmalade
Boy) and AIC (Tenchi Muyo, El Hazard) studios a few weeks
or months to sell their cels after they finished airing 
the episodes on TV.  Some studios may never release their
cels to the public due to various factors.  For example,
many sponsors and investors of the shows don't permit the
anime studios releasing the cels to the public, a good
example is Evangelion.  You may find the production
cels for EVA, but they're stolen ones, and yes, they're
very expensive.  That's why you see some of the cels in
the market are particulaly expensive and rare, just
because they may be the stolen ones from the studios.