The largest complaint I hear from most contractors is their inability to get good workers. That situation hasn't improved with the current low unemployment rate, combined with what is fast becoming a shortage of immigrant personnel.
One source you may not have considered are your former employees, often called "boomerang" workers. This is yet another reason to maintain a cordial relationship with employees when they leave you for what they perceive as a better opportunity. Especially when a past worker is one who has shown they are diligent in their job, why not ask them if they might want to come back?
Each of us makes decisions based on our personal needs at the time. These may change over time, of course, and a previous work environment may look better with the visibility of hindsight. If you have created a great work environment at your organization, that should lend confidence that if circumstances have changed for the employee then coming back to work for you will appear attractive once again.
Today, with the advent of social media, it has become possible to keep track of former employees via a professional site like LinkedIn. When they have new accomplishments be sure to congratulate them. You may even learn they have gained new skills that will make them and even stronger employee for you now than they were before.
If you do try to entice a former employee back to your firm, be ready to tell them why it will be good for them to come back, not just a plus for you. There is a natural tendency to feel that returning to a former employer is a step backward in a career. It will be up to you to show them why that is not the case. You may also want to consider if there are any benefits you might be able to provide them to confirm that returning to work for you will be a positive for them and their family.