Check out ycombinator cofounders. I haven’t yet found a cofounder here but have learned a lot from the conversations I’ve had with people on the platform.

Start talking with people. Choose something that you have skills, knowledge or experience with. People love to talk about there problems. Reach out to people on LinkedIn, visit local business, etc. During the first few meeting you will just be developing your questions.

As you conduct more customer interviews, you will gain a better understanding of the problems experienced. Once you have more than a few people talking about the same problem, this can be the opportunity you are looking for. Then the hard work starts!