In my experience, there's no substitute for putting in the hours of painstaking research: scouring job boards and sites like levels.fyi for companies you haven't heard of yet, exploring their websites, looking at the professional profiles and blogs of the employees, etc. Every once in a long while, you find something really legit - places like Brilliant, McMaster-Carr, Bitwise Alchemy. IMO the better the place the more likely it is to be somewhat under the radar