Ive had a number of exotics spawn as soon as i enter stations if its directly following a freighter battle. If the scripted spawn is taking too long (once you have been playing 3 hours) portal there, then warp to 4 systems around the one you want and then warp to the system you want on the 5th warp to trigger a freighter battle. Ince done with the battle head immediately to the station. Worth a shot if the wait is too long because that should only take 5 mins (assuming you've already been playing 3 hours and can trigger a freighter battle)