When assigning users to a listing, there is an option to restrict the number of users to a maximum number. BUT a team doesn't count as a user and the number of users on a team don't count either. So the only option is to individually assign the users to the listing.
But when you're talking about 500 ish users, the process is untenable. If the process to add users was better, it might be possible. But the window is sooooo small, and you can only see 30 users in the list. Please make this easier!