So does the cable company, water company and phone company. Because businesses have turn over of personnel. People don't stay at jobs like they once did. They canvas neighborhoods. Every house within walking distance of your house should have your business card.
People enjoy supporting their neighbors.
You are in the same boat they are. They identify with you. Work your neighborhood and it will work for you. Just pin your card to these boards on a regular basis. Many people check these boards on a regular basis.