[Improvement™]

If I understand correctly, you mean something like this?

BlackPlayer (skinid 1)
OrangePlayer (Skinid 3)
PurplePlayer (Just Connected is in class selection)

Class Selection for PurplePlayer:
Skinid1 (Has been taken, Please Choose another one)
Skinid2 (will respawn.)
Skinid3 (Has been taken, Please Choose another one)
Skinid4 (will respawn.)
Skinid5 (will respawn.)

If so then, use the OnPlayerRequestClass Callback, never tried to make something like this, but perhaps you will be needing variable's to store if the skins has been taken. Or perhaps assign SetPlayerTeam ids on OnPlayerSpawn Callback and check them with GetPlayerTeam function.