Another thing I've found is that the corals that are rare, are usually rare because they grow so frigging slow. Jason Fox sets up some pretty rare stuff at the NCPARS/TFP frag swaps in PA but I just can't justify $100+ for 1 inch of coral that will take 2 years to become 2 inches. Most of the people who look at my tank have NO idea what's "rare" and what's not...they tend to miss the rare stuff because they are so small.
But to answer your question...The right frag swap will pull in the vendors with rare stuff as well as home reefers that will sell a frag or two of their rare stuff, but don't expect to see them at the swap unless you've asked for them.