In our area the local bee club has a swarm list that includes the names of people who sign up to catch swarms; perhaps a club in your area offers something similar?
I also know on one Facebook page (this one is dedicated for keepers in our local area) that posts swarm finds. Of course craigslist is always a common resource but I don't know how much people ever go there to find a swarm catcher.
One other idea; register yourself as with local police and fire departments; in our area that is a very common method to get swarm calls as people often call one or the other.
Hope these help,