Researchers interested in knowing whether a business provides its employees with a 401k retirement plan can find out by searching for the legally mandated and publicly available Annual Return/Report of Small Employee Benefit Plan, known also by its number -- the Form 5500 or Form 5500-SF -- here. If an employer has established a plan and filed the mandated form, researchers reviewing the form will learn the employer's tax ID number, how many plan participants there are, how much money is in the plan and when it was established. A comparison of employee contributions to employer contributions will yield the employer match rate (or lack thereof.)
Less specific but larger data sets are also available for search and download. And, look here for a very well written guide to the online Form 5500 search engine.