I went and looked, but there aren't any good anonymous file sharing services that allow this sort of collaborative thing, not any that I could find for free anyway. I'd host something myself, but its a lot of work for something that has like 2GB of storage max. Best bet is to use the forum here and just tag your post with something like "#customNPC" so people can use the search function and find them all in this thread. And maybe add a picture or two so people know what they're downloading.
I've seen other games on this site with linked forum pages for stuff like mods and fan art stuff. maybe it could be something like that, a dedicated page for NPC sharing, not sure if that makes sense.
also it would be cool if the game had a menu to see all the saved NPCs (to remove the ones you dont like for example). some people would also like to edit NPCs (rn you can edit presets but not NPCs). i can totally imagine someone liking an NPC but wanting to modify the sex or other details.
lastly, i'll reupload my (updated) cheetah characters, both male and female version, both presets and NPCs