Generally speaking, I wouldn't search for bootstrapped but rather sustainable. Plenty of companies that raised a seed and become profitable. Just that the current situation of the company would be a reveal during the interview where you should ask whether the company is profitable or what is the runrate and plans for the next round. Nonetheless, here is one resource: - https://peoplefirstjobs.com/

I was thinking about creating something similar for ages, regardless of profitability or money. There are so many great companies out there.

Speak to an independent tech recruiter/agent who deals with many clients and tell them that you're looking to work for a bootstrapped startup. Those who work with startups usually know their backstory.