I’m the vendor coordinator for my local Mensa group’s annual convention. Our con (called an “RG” or “Regional Gathering”) draws 500+ Mensans to the Sheraton Chicago Northwest in Arlington Heights, IL. It is the largest regional convention in US Mensa.
You can get more information about the convention here. If you happen to have a craft, service, or product that you’d like to sell to the group (or know someone who does), please feel free to get in touch with me, and I can provide you with all the details.