Kero-chan is decently easy to find. Even in 
his "adult" form, he's not too bad to find - 
there is at least one at Asylum Anime, as of last 
I looked.

Suppi is another story. . . There is one "okay" 
cel of him on Yahoo Japan. I haven't seen another 
in a while. In his adult form, he's pretty hard 
to find (although not impossible). . . When the 
perfect one popped up on Yahoo Japan, I finally 
just bit the bullet and bid hard for it. Paid a 
bit much, I'm sure, but when it's a character of 
which you only want one cel. . . (*shrug*)

Many Sharp Smiles,
--Drac