A client at work which is a local property management company (big enough to have 2 part time employees and one full time property maanger) lists all of their properties on Craigslist as well as many more commercial sites, so it’s not just mom and pops on there

Edit: another option is to call up a given property during business hours to ask about availability. Chances are your call will go to the property management company and they’ll have more properties than just the one building you saw the number on