We are hoping to offer a trade block for the 2020 season, but cannot guarantee that it will be available then. We're working on a massive offseason to-do list and we are hopeful that this can get done in time.
In the meantime, a workaround would be to add a player nickname as "on the block" to each player.
It will look like this:
We're also hoping to have a feature that allows users to counter trades. Check back later this offseason!