Wow what group was this? Must be quite a few members.
It's a facebook group that I'm in... there were 128 people who participated. I made approx. 80 trades for this swap! This swap is U.S. only, but I have seen some that will do international trades... but I have no idea what the restrictions are. I know that many countries don't allow it.
They was this one was organized, was that all exchanges took place through a "host".
We made lists of seeds we had, and seeds we wanted.
The swap had a start and end date.
Post your lists at the start... then everyone just checks over each others lists and you message back & forth to work out your swap with each person you wish to make a trade with..-- and keep a detailed list of each trade you agree to.
Then after the swap end date, you package up all of your seeds that you are trading, and everyone mails their seed packages to the same person, the host. (Including a prepaid shipping label for the return package/postage.)
The host will then open each package, and sort out who gets what as per the trade lists, and then mail the finished and sorted packages back out.
This way no one is revealing their home address to anyone except the host. And you only pay to shipping for one package to go out, and one package to come to you.
There are many sites that do seed exchanges. Some are much better than others. You would just need to sort through a few of them and find one that sounds good.