if you feel called to start your own, they have guidelines on how to get started. its all Do It Yourself! :)
I have friends who do a more cooperative type of swap, its smaller, between themselves and not open to strangers. It could be as simple as a monthly (or once a year!) barter.
For the soup swap parties Ive had, its usually been 7-9 people and mostly from my homeschool group. I havent opened it up to more people, just emailed my friends! :) but it was fun to try new soups I dont usually make.