Generally, what you'll find are either guides on "how to write a business plan", or sample business plans for fictitious companies. If you're looking for real plans that real companies have written, that will be harder! These will most likely be proprietary, and hidden away from public sight.
The one exception may be the compilation Business Plans Handbook, published in many volumes by Gale Cengage. But in the introduction, there is the following warning:
"While the plans contained in BPH are real plans, the majority have been fictionalized to protect confidentiality. Personal and company names, addresses, and sometimes product names were changed to protect the contributors. Additionally, in many cases financial data or charts were removed to protect the owners' privacy."
Business Plans Handbook is available online in the database Gale Virtual Reference Library. Because of quirks in the interface, you have to search in two separate sections: the 1993 - 2011 volumes, and the 2012 - forward volumes.
Below is only a sampling of the books that we have in the collection. There are suggestions on searching for more books in the box above.
Below are links to some relevant, and narrower, subject heading searches in MARQCAT. These are just some of the possible subject headings you can use; the broader subject heading 'business planning' is also relevant, but brings up a huge number of items, some of which are much more general in nature.
Also below is a link to a keyword search that works well ...