[–] sakuramboo 0 points 1 point 1 point (+1|-0) ago
There is no central database but spread across all of the internet.
Search around for Creative Commons Cartoon Characters or Comic Character or something similar.
Public domain might be a bit harder because for something to be entered into the public domain the can't be an ownership and has reached a certain age. Creative Commons would be easier to find.
[–] firecat ago
Tv Tropes may be the place to submit and look at characters in Public Domain. Though you may need to put effort on the character's backstory and such.