Contact local chapters of fraternal organizations like the Kiwanis, Masons, Elks, or Lions Clubs. Reach out to veteran's organizations or contact retiree groups from traditionally male professions such as auto and construction workers, engineers, doctors, and lawyers. Use men as part of the recruitment team. Men can more easily see themselves in the mentor role when the recruiter can talk first-hand about the experience. Use photos of men in promotional materials.
Photos showing only women make it appear that only women can be in the nurturing role.
Assign male volunteers to groups with other men. When conducting trainings or meetings make sure that no man is assigned to a group where he is the only male.