Check Van Eaton Galleries. They're the best bet for any 
1980's cels like Tranformers or GI Joe. http://
www.vegalleries.com

It's kind of surprising more Jem cels aren't out there. There 
have been a ton of G.I. Joe and Transformers cels showing 
up at Galleries and on eBay, but relatively few Jem cels. 10 
years ago, Jem cels weren't that hard to find. 

Kett