Recruiters, also called headhunters, are often misunderstood as to what they are, what they do and what they are looking for.
Most people, particularly in upper level positions, think that the only way to find another good top level position is through a headhunter. That appears to have historical value at least for the other guy. Don't get this mixed up with being headhunted which is where your name has come up and you are being offered a deal to leave your current position and move to one being offered.
So let's look at headhunters. A headhunter is engaged by a company to find the right person for a specific job. This person is given specific skills and qualifications. She is paid by the company. Usually, she is only paid when the job is successfully filled and not until. Sometimes, a headhunter may be kept available to a company by being paid a retainer.
Therefore to make money, she has to make the company who has hired her happy by finding the right person for this position. The company in this case is her employer and therefore her focus - not the people looking for a job.
There are some headhunters who operate within a large company and may have several job openings that she is working on at one time. If she is working out of a small company then she may be working on just one position. She will not have hundreds of job openings like an online job board will have.
Because of the limited jobs, her focus must remain narrow to only those candidates that match the job openings she is working on. Anyone else who doesn't match the job criteria is a waste of time that she can't afford.
Also keep in mind that a headhunter usually operates within a specialty, such as sales, or finance. Therefore, if you send out resumes to these people but they aren't hiring in your field, it's a waste of your time and theirs.
To increase the odds of finding a headhunter that specializes in the same field as yours, you need to contact multiple recruiters in the hopes of finding one that has a position that might match your qualifications. How do you find these people? There are several options. The free option is to use the Internet and Google to track down as many as you can find.