To be honest, many people will want to get together in a landlord organization just to trade stories or socialize. That could be a good way to get people into your organization. Nonetheless, there are also a lot of other productive things a landlord association can do.
Good help is hard to get.
You can do listings, possibly noting references from your membership, etc. Leave time at the end of or after each meeting for story swapping. You may want to periodically have a pot-luck or barbeque or some other strictly social event. Almost everybody needs the socializing. Some people will come only for that and that activity will help unite the organization for times when you need power in numbers.