Here is a link to the Trading forum here
http://www.tomatoville.com/forumdisplay.php?f=65 You can browse the lists and see what many are offering and what others are looking for in the way of seeds.
Then if you are currently growing any open-pollinated tomato varieties now is the time to learn how to collect, save, and store your seeds so that you will have seeds for trading next year. Here is a link to a good basic How-To article.
https://www.mastergardeners.org/pdf/...mato_Seeds.pdf
Dave