It's a common conception to think that people attended the Association's annual gathering for building connections or sowing agendas. That was true, of course, but the real reason people came was for the event of the third day; the auction.
There were several auction sites in the Eastern Federation, and even more in the continent. There were those established in the black market too. But the one held at every annual gathering was considered to be the biggest of them all.
It was a fixed event, so there was no need to advertise it. The fact that the most prominent and wealthy espers would gather in one place made the supplier and owner of the auctioned goods save their best products for this event. From artifacts to rare potions, even collectible items from the era before the age of the apocalypse.