It's not surprising it's hard to find. I think it helps if you are working in a place that rewards such initiative. In my experience, it is not always the case. How do you even screen someone for self-teaching and self-motivation by the way?
Self-teaching can be measured through asking probing questions about what the candidate does to keep up with new developments in their field. Self-motivation is harder to get at, but sometimes it helps to ask about what the candidate looks for in a role.