Look to the news.
FEMA has a pretty good photo library.
I know it's "Emergency Management," but the photos are of homes and businesses and can help you make your point about preparedness.
I would have recommended that you "show the colors" to get people thinking about BC, but I gather that those 49k people are scattered over a wide area. If thre are local/district practitioners or even people assigned BC functions, you might suggest they do "walk-arounds" to be seen checking "things." People notice (or that has been my experience).
Can anything be done to raise awareness on a local (store) level - perhaps a sho-n-tel or QnA with the staff to see (a) what they know about BC, (b) what they think are the threats and mitigation options, and (c) what role they will play if something goes "bump in the night." If you can get management to spring for some goodies, maybe even little gifts or at least snacks/junk food for the participants, all the better.
It also would boost the image of an 800-pound gorilla (or two) from HQ made an appearance to wave the flag, but that may be too much to ask.