I can't seem to find any other chameleon than the Disguise Chameleon in Oslya. I don't know if I just can't find them, or they're not there. I've gone through the whole map with plane, entered every cave. Nothing.
I'm too weak to walk there (north areas) by feet and check random battles so I've checked only southern and western part.
Having a signature is like keeping a gremlin.
Just don't overfeed it, don't make it wishy-washy and you'll be a good responsible Signature Keeper :]