If you're struggling to find great agents, the most likely offender is the quality of your job ads.
Most people fail to appreciate the role a compelling job ad plays in finding the best candidates. Some suffer from a little too much egotism (e.g., "They should consider themselves lucky if we hire them."); others are old-school (e.g., "In my day we didn't need to be courted"); and some just aren't great writers.
Regardless of the reason, what you write about the open job you have — and how you write it — has a significant impact on your ability to find the right people.