Yes, it's difficult to find a co-founder in general, regardless if they're technical or not. I think it's similar to dating in that respect.
You end up looking for someone that shares common values, principles, goals, and dreams. Finding that match takes time or luck. You have to be patient, but also get out there and look for someone. Most importantly, you can't beat yourself up when you don't find a match right away.
Trust me, when you find a match, it's like finding a partner in life. When your building something together, things just flow so easily. That doesn't mean you don't disagree or debate about direction. It's just that those debates are so much easier to overcome. The longer you work with them, the more in tune you become.
I think the people you work with is the largest determining factor of success, so it's so critical to get to know someone before committing to a project.
Ray Dalio has written a lot about work relationships, so I'd suggest reading the article below.