Would be too shocking if I consider this a "How to find a non-technical co-founder" question?
Because I think that is just what you need. I don't think a freelance, temporary or part-time marketing person would be a good choice. A real co-founder, responsible for marketing your product would be ideal. Someone that could hack the distribution part of your product.
Actually, I don't have any practical tips of how to find this person, but my advice is that you should think of her as an essential part of the team, not a disposable labor with a specific mechanical job. Don't be the "code guy" versio of the HN stereotyped "idea guy".
Maybe something you could try is trying to find, on startups' events, that non-developer young guy, who is kind of lost there, not pitching any of his ideas, just trying to understand this environment and learn a few things. My guess is that this persona, with the right potential skills, could be a good distribution co-founder.