Ask your friends and aquaintances if they have used search firms. If so who do they recommend you use and who should you stay away from. Keep in mind that you will pay a healthy fee when using a search firm. If you are using a firm for the first time, negotiate a lower first time trial use fee and let the firm know if they do a good job you will use them again. Identifying and hiring qualified high performing employees is one of the most difficult tasks of the business world.
Employers simply have to be aggressive in their efforts to locate good people.
Look at your current hiring practices and modify them to become more efficient and more aggressive in locating good candidates. But, be selective in who you hire. Even in a tight labor market you are better off leaving a position open than filling it with a marginal employee.