One place you could look is https://www.entrepreneur.com/article/281416

Another place you could look is in the virtual library.  You can type in "Business plan" in your search box, and right away, there is a research starter all about business plans, by Salem Press Encyclopedia.

There is also an eBook available in the Virtual Library, called

Business Plan Checklist : Plan Your Way to Business Success

You can type that title in your search box, and get that eBook.

These are the best ways to get started.