I'm not sure there's a simple formula for this one. I've seen in past experiences the most successful co-founder situations result from networking within a small community. If you can meet someone through a friend, your chances of success increase dramatically. If that's not possible, another option is attending MeetUps for specific interests (like software development or specific coding languages). The final suggestion I have although probably most difficult is joining startup weekends, getting on a team with some technical talent, and seeing how well you mesh together throughout a long working weekend.

I'm personally a huge fan of the DISC personality test. It's short, direct, and always has an accurate result in years of experience. You can find the test inexpensive online or buy a license to print and distribute yourself. I know specifically that Sales is one of the potential personalities so it correlates directly to what you're looking and evaluating for.

In every business I've ever been apart of, it has to be customer service. From the very earliest times, treating every interaction with customers and potential customers proved invaluable. Paying extra careful attention to their needs and problems allowed us to turn them into our biggest advocates, which in turn result in free marketing (the best kind). Repeating that only cost us time, but yielded more than if we would've invested in more traditional marketing mediums (like SEM).