Many job seekers send out "mass mailings" of their cover letter and resume to a variety of companies whether they are aware of a job opening at that company or not. This is not the most effective method of job seeking, but it can be used with some success.
To make it the most effective, you should carefully research the companies you are interested in targeting. Prepare a cover letter and resume that speak specifically to the needs and expectations of that employer. This means that each cover letter and resume that goes out must be tailored to the employer and to the job for which you are applying. There are a variety of resources available for researching employers, including employer directories, chamber of commerce information, company websites, and local newspapers On-line versions can be particularly effective for research. Here are some you may want to try.