The previous answer has some good ideas for finding out about the identity and location of potential local competitors. However, it is important to realize that it is not enough to know who your competitors are and where they are located.
Typically, when someone is creating a business plan, they need to include a section on the competition. They need to have as much detail as they can on the competition. They need to be able to, for example, describe how the competitors' products compare with the products they hope to sell. They need to understand how much the competitors are achieving in the way of sales. In other words, they need to know much more than where the competition is located.
Of course, all of this can be exceedingly difficult to obtain. One thing to do is to actually go to the competitors' places of business. You can look at prices and try to gauge how many customers they are serving in a given time. You can watch how their service staff interact with customers. This can give you a sense of what you are up against. (You can also look at their websites, if they have them, to find out what they sell, what prices they charge, etc.)
Another thing to do is to attend local trade shows. Your competitors might be there trying to make more people aware of their business. You can pick up any information they make available.
You can try to talk to people who might know about the firms. You can ask around among your contacts to see who does business with the firms. You can talk to the firms' suppliers or customers or employees. Of course, it is quite possible that these people will not talk to you. However, this is an important way to try to get information.
Obtaining enough information on competitors to create a business plan is very difficult. You will need to try many different tactics in order to do so.
The research skills you are learning in your university classes can be applied to business. Your first step in business, as in writing papers, should be going to the library. First, you should consult the Yellow Pages, as it normally has listings of all local commercial telephone numbers organized by type of business. Next, you should go to the Chamber of Commerce, which also maintains listings of local member businesses. Next, do a very thorough set of searches on Google and Mapquest. Finally, the single most important part of your research, is walking (not driving) around the neighborhood, covering in meticulous detail the area centered on your potential business location.