I've usually found my mentors at work in the past, but you mentioned that your opportunities are limited in your startup. I've mentored many people myself and since I left my job at Amazon, I've been mentoring on mentorcruise.com. There are a few other platforms that do it as well. Yes, it costs money but it's an easy way to test-drive multiple mentors.
Regardless of how you find the mentor, the key is to make sure the relationship is a good match. It's easy to get caught up trying to work with the "smartest" person. But, you want a mentor you can feel at ease with.
Regardless of how you find the mentor, the key is to make sure the relationship is a good match. It's easy to get caught up trying to work with the "smartest" person. But, you want a mentor you can feel at ease with.