This is hard because people tend to go on line to purchase gear. One of the things I have done in the past is get involved by going to events sponsored and put on by the shop; dive clubs, clean up dates, gear demos. I used to help out with cleaning gear and whatever else needed to be done; essentially volunteering some time. I also referenced new divers or people interested in becoming a new diver, to the shop. I would purchase some of my gear through the dive shop as well to help support them.