There actually will be an Anime/Sci-Fi/Comic Expo 
coming up the weekend of the 19th of October. I 
haven't been to it before, but it doesn't really 
sound like a cel convention. I'm not sure if 
there's a separate cel collector's area. The 
guest list seems kind of slim right now, so I'm 
not sure if I'll be attending. But you can check 
out the official website here:

http://www.hobbystar.com/boston/index.html

Tony