How do you look for references and inspirations? [on hold]

I work in a UX consultant company so I'm doing many types of UX project for various companies and I'm always looking for good references and inspirations:

  1. For competitors of the company I'm designing for.
  2. For examples of complex behaviors such as link diagrams, advanced filtering, Boolean search etc.
  3. for general apps, systems or platforms that have similar features/goals.

how do you look for such references/inspirations? what do you do if you find a similar system as inspiration but you can't simply sign up and use the product (because it is design for professional customers)?

thanks!! :)