One of the most important activates of a leader is talent development, which includes recruiting people with leadership potential and managing their career paths. You have to create challenging opportunities for relatively young employees and provide them with visibility to the senior management. Company structure could be help meet some of these goals: for example, some degree of decentralization could help push responsibility to lower levels. This would create more challenging jobs for managers with high potential and also provide with an opportunity to prove they are able to handle added responsibilities.
You can also help your with leadership development by creating programs to develop employees technical skills and develop their emotional intelligence. This can be done either through internal training programs or external coaches or consultants. Executive coaching programs have proven to be successful in a number of organizations.
The best way to encourage managers to participate in these activities is to recognize and reward those on your staff who successfully develop leaders. Make that an important factor in performance evaluations and decisions about promotion for those managers, especially to the most senior levels. This would help create a corporate culture where people value strong leadership.