To find all the players who have not been put on a roster you can run the report titled "Rostered/Unrostered Players." You can also determine if they are on a team by viewing the pending team column.
Korrio Team Builder was designed to provide you with the information you need to roster players to a team. In Team Builder, once you select a program, only players that have not yet been rostered are available on the list to be added to teams.
However, to run a report on those that are not rostered, click on the Legacy Report titled Rostered/Unrostered Players under Program Reports.
The default column to show if a player has been rostered to a teams or not will be the Pending Teams column. Reminder that the term “Pending Teams” in Korrio refers to those teams that have a Season Start Date that is in the future. This feature allows registrars to roster players in private. Players that have a team name listed in Pending Teams means they have been added to a team. If you do not see a Pending Team name listed, this player has not yet been rostered to a team.
However, to be sure they aren't on a Current Team, you can use the Customize Your Columns feature to remove Pending Teams and insert Current Team.
You can also add the Last Historical Team field to view the last team that the player had been rostered to.