The primary, even the usual incubator of vocations is the family: strong, loving, mentally healthy, and deeply Catholic families. Although some of those certaintly still exist, they seem to be far fewer than they used to be. I believe that is the main reason why there are fewer priestly vocations these days than when I was a boy. But since John Paul II became pope, the vocations picture has begun slowly to improve, even in the midst of the sex scandals. One of the factors behind that is The Serra Club.
It's a lay organization whose purpose is simply to foster priestly vocations. They do it primarily by joint prayer, friendship with men considering the priesthood, and financial support for seminarians and seminaries. Upon her retirement, one member I knew in the 1990s sold her business and contributed a substantial portion of the proceeds toward scholarships for seminarians, thus enabling several young men to attend seminary who would not otherwise have been able to. I've never been a member myself because my commitments have rarely permitted me to attend meetings. But I hope that changes soon, and I urge those of you who care about vocations to join and participate if you can. There are chapters in every major diocese and many smaller ones. The web site provides the needed contact info, and most chanceries can put you in touch too.