The server sends the co-ordinates of players if they are ~150 blocks away from you. Tracers/Radars show these players. It's impossible to get the co-ordinates of other people as the client wouldn't have any information on that player. Even if you forced your client to load chunks extremely far away, it still wouldn't work because the server wouldn't have told the client any information about players in that region. It does seem like a cool thing in a griefing client, but unfortunately its impossible.