If the firm is "publicly owned by shareholders", they are required to disclose financial statements annually and either quarterly or twice a year. These filings are made with the Securities and Exchange Commission (SEC) in the US or with similar agencies in their home country. They are accessible on the company website, on the agency site or through the resources listed below in Excel format
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.