Think of this as a sort of big brother/big sister type of operation. You need to develop mentors with the ability to meet new people, assess their skills and interests, and then develop a productive relationship with that new person. In this way you will be able to grow a whole new crop of firefighters for your department.
This should not be terribly difficult. However, I need to stress that the people in your mentorship program need to be willing volunteers. The last thing that you need is a disgruntled, angry person influencing your new members. Make requests for mentors, not demands.
Once you create this program, keep an eye out for those people who can naturally strike up a conversation with people. Some people are just comfortable in interacting with others. Once you have made a few selections, assess their skill levels and see if they have interest in helping others. You may be surprised at who steps up to the plate on this issue. Some people might not naturally volunteer, but would be pleased to be asked.
Anyway, do not leave the future of your fire department to chance. Decide today that you want to make a positive change in how you shape the development of your new personnel. Let me close with a simple thought. Perhaps you can improve the retention of veterans by creating opportunities for new friendships. I could be wrong, but the successes I have seen with programs like this tells me I am probably right.
Why not take the time to create a mentorship program in your fire department.