If you know all of these except for Marketing, say, then this is where you will need to invest some time and effort. You can find a wealth of information by utilizing the traditional data sources such as chambers of commerce, major cities' websites, trade associations, the US Census Bureau, trade journals, magazine and online articles and advertising, etc. Performing keyword searches on Google, or Ask will bring up websites to check out. Following are some places to start:
Internet Public Library - The Census Data and Demographics (ipl.org)/: An especially useful site that has links to information about countries other than the U.S.
However, the best business plan template is that which meets all your business needs and requirements by offering you a high level of customization and a professional layout of all the content that you would like to include.
At this point, you may be tempted to skip writing a business plan altogether, viewing it as an unnecessary exercise in jumping-through-the-hoops, suggested by some old business professor who probably never held down a "real" job anyway.