Yes, they are rare.  *cries with you*  Sadly, the 
fire that burned down the studio took most of the 
cels with them.  *sigh*  Your best bet is the 
newer series, but G1 cels occasionally pop up on 
ebay.  Also, if you ever get yourself to Botcon, 
they occasionally have them for sale.

You could try hitting up some owners of G1 
cels, but trust me when I say, most people aren't 
willing to let go of them.

But good luck, my fellow Transfan, happy hunting. 
^_^

-Chaotic Serenity