Immersion. Work in the industry at a position where you're likely to encounter inefficiencies. In healthcare, for example, you can't spit without hitting an optimization opportunity. Working midlevel can mean you get to see low-level workers hacking around bureaucracy and management wringing their hands about money and budgets and such.

Taking a job in an industry to get access to its seedy underbelly isn't super appealing to most founders, but for some ossified industries there's really no other way to find those golden opportunities.

Oh, and be patient. Practice being a mouthless set of ears.

I am not in this space, but my guess would be this sort of company was started by people with an intimate knowledge of the specific space & what they can & can't do, so as a strategy, you're probably best off working in said industry and finding that niche that needs a solution.

Yes. Become and expert in the field by spending many years working in it in many different roles.

From the outside? Probably not.

> ... profitable _symbiotic_ niches ...

Fixed it for you.