I found good luck talking to the individual store managers. They know that the stores need to be cleaned, they have to walk on their nasty sidewalks everyday. I would push your services to them, and from there they will "hound" the right person and if everystore is pushing for pressure washing services and they all have your business card - your in.
I wouldn't "just wait and see". Follow up in a week, again a week or two later. Keep checking back every couple of weeks. Stay on this guys mind without hounding him and you stand a good chance of being considered. Good Luck!!
They don't do regular service they only call when they need you.