When you look at someone else's Plant Lists, check "View Only: Have". At least then you know they do have them. If they set up categories, there will be a list of categories on the far-right. Hope they made one category for "willing to trade".
Alternatively, check out these forums frequently, looking for Want Posts or Offer posts:
Plant and Seed Trading
Co-ops, Group Buys and Classifieds
You can post lists in Plant and Seed Trading of what you offer, and what you are looking for.
I like to keep easily edited, hopefully searchable lists somewhere, and then keep a link to hem in my signature block.
When you go into the Plant Database and list a plant variety that you WANT, other people who look at that plant in the database will see your name as "Wanting" it. They may contact you.
You can make you lists more "trade-friendly" by creating multiple categories. One such category could be "Plants available for trading" or "Seeds available for trading".
Then also make a category for "Plants I WANT to trade for", or "Plants I REALLY Want a lot".
Then when people look at your list, they can click on a "category" on the far-right, instead of the "Have, Want, and "Used To Have" check-boxes over on the left.
For example, I have these categories:
