ATP has two forums that can also be used when looking for plants. The Classifieds and Group Buys forum and the Plant and Seed Trading forums. You can place ISO daylily listings in either forum depending on if you want to purchase or trade. I do check both regularly(several times a day) and add new daylily listings from them to the Daylily Classified sticky here at the top in the Daylily Forum. If you are going to post in either of those threads you can also send me a tmail to be sure I don't miss adding your listing and updating the sticky.
A year or two ago we also did a spring trading thread in the Daylily forum where folks listed the daylilies they had to trade and what they were looking for. We could do that again next spring if there is enough interest in one.