Although each church is unique, there are a few things all churches have in common, one of which is the challenge of finding ministry volunteers.
The Challenge of Leading Volunteers: Seven Ways to Boost Volunteer Engagement is a free eBook by Don Simmons & Steve Caton. One of this e-book's main points is that volunteers are people with whom you do ministry. You have missed the point if you ask, "How do we get more volunteers?" rather than, "How do we make more disciples?"
When a church has a healthy ministry, it will naturally produce healthy volunteers. A church that struggles to identify and empower volunteers probably struggles in the discipleship area as well because discipleship and volunteerism are connected.