It's pretty hard to do this "easily" if you don't 
know the language well.  Here's what I do...

On Celga's search page, there are ten or 
so "Miscellaneous" links.  I've been informed 
that they are organized alphabetically, with 
respect to the Japanese alphabet.  What I have 
confimed is that cels for individual series that 
I'm interested in do appear in only one category.

So, I plowed through all of these pages every 2 
or 3 days for a couple of weeks, and made up a 
little crib sheet of which series are on which 
miscellaneous pages (e.g. Gokudo is in 
Miscellaneous 2;  Outlaw Star is in Miscellaneous 
3).

Then I manually look through the specific 
Miscellaneous pages that contain the things I'm 
looking for.