What are some places to find one? How do you know he/she would be a great co-founder for your startup?
The guy from software engineering daily just launched that "Find Collabs" project recently.
You should try posting in our co-founders group - https://www.indiehackers.com/group/looking-to-partner-up
I always say co-founding is like a marriage, you should get to know anyone you go into business really well before signing any long term papers!