Yup cels exist.  At one point there was an 80s 
cel website of a collector who had Jem, D&D, and 
GI Joe.  She must've cornered the market on 
them.  Unfortunately people kept pillaging her 
images and she closed down the website.  There 
was word that it would reopen but I don't think 
that ever happened.  I once asked her about where 
she got some of her cels (primarily the Jem ones) 
but all the info I got were the usual sources 
(Ebay and a few of the art galleries which no 
longer had them).  Anyway, not sure if this is 
too much help to you but the cels are out there.  
Good luck and happy hunting.