We did a collection drive with a Unitarian Universalist church in town. The congregation was very supportive and mentioned us in their newsletter as well as during a Sunday service. The collection drive was set up in their parking lot on a Saturday afternoon and brought in about 40 bikes, though most of them came through our own promotion efforts.
Some (if not all) Jewish synagogues require a community service project as a requirement for a Bar or Bat Mitzvah, and a bike drive would make a good one. You may wish to contact area synagogues and ask them to recommend your organization to families looking for a project.