I can attest to this.  I have been looking for
a Part 1 cel of Eve for so long I've practically
given up on ever finding one.  The only one
I have ever seen for sale was the one at Robert's
Corner Anime Store.  The rest were held by
collectors not about to give them up.  This is
really disappointing to me because Eve's my
favorite character.  BTW, Yann, one of the cels
in your Eve OVA I gallery is actually from Part
II (close-up with mike).

Regarding rare cels, it seems like everything
I would be likely to collect is rare.  :P  I've
also been trying to find a nice shot from
Windaria or Leda for a while.