Public companies in the United States are required to file financial information with the Securities and Exchange Commission (SEC), through the EDGAR system. Non-US companies are required to file with agencies in their home country and may also file lmited filings with the SEC. Find public company filings on the company investor relations webpage, SEC's EDGAR system, or through Horn Library resources.
Companies that have not issued public shares do not have a requirement to file full financial data, so the information about them is private and very limited. Sometimes they will release a certain amount of data on their website or with a local financing agency, but that is rare. Try these resources:
All US non profit firms must file with the Internal Revenue Service yearly and their Form 990 shows their operating financial data and other salary and operational information.