Skins
Custom NPC skins are something that many server admins have asked for ever since Citizens was first released. Unfortunately, skins are handled purely on the client. This means that, without a client modification such as SpoutCraft, NPC skins are not controllable. The client decides where to look for skins on the Minecraft skin database.
But what about giving the NPC a "display name" and using the real name to find the skin on the Minecraft skin database?
Again, this is not possible. Many people have suggested that we give an NPC a "display name" similar to that of Players. Unfortunately, display names are only used for chat-related things. An NPC has no concept of a "display name" that would have any effect on its skin.
So, I've ignored everything you've said. I just want to know where I can go to get custom skins.
To get custom skins for NPCs, you must download SpoutCraft. There are other client mods out there that control NPC skins, but many of those are proprietary and/or outdated. After installing Spout on your server and SpoutCraft on your client, install CitiSkin.