... that might take quite some time... Though there are good roads
I would recommend to travel from Amn to Cormyr by road and then take a ship to Aglarond. Either in Cormyr or latest in Sembia, somebody should travel into this direction. You could also make a journey to Chessenta and then travel to Aglarond. Anyway shipping would reduce travel time enormously
'You see dead bones? ... I see an army!' Ezechiel 37