Create a simple flyer (often done for website/SOCK publicity) and circulate to all members to display
in workplaces, gyms, running clubs, other sporting clubs, schools, public notices, free website publicity etc...
(There was a great article in the most recent CompassSport about increasing awareness of events within the local community.
For me the key to increasing numbers is more locally available events, decent marketing/publicity, competition/accomplishment (at whatever level).
The issue of whether our local events can support larger numbers is another issue...