It can be difficult to get information from a private company, but all businesses have to interact with the government in order to operate, so public records requests can be just as useful to a business journalist as it is to any other reporter.
The Arizona Agenda created a zine two years ago on how public records work and is an excellent place to learn more about how to request public records from government agencies. The printable zine includes tips and tricks on how to get records, what kinds of things are made public, and what you can do if an agency is stonewalling your request. They even include a template to begin your own records request.
Another option for starting a public record request is by using a letter generator like the one offered by the Student Press Law Center.
The Reporters Committee for Freedom of the Press offers the Open Government Guide which compiles open records and open meeting laws for every state. This guide also allows you to compare laws between states.
You can also reach out to your state Ombudsman (a public advocate who is an official member of the government specifically designated to investigate or file complaints against the government) for assistance or resources. For example, the Arizona Ombudsman recently updated its Public Records Law Handbook and tracks and compiles requests and changes to these laws on the website and has a FAQ specifically for journalists.