Hi there, I found this list of all teachers and there whereabouts on a German fansite and I can confirm it works.
Just be patient eventually they do show up.
Battle: Pensecola - Providence - Gibraltar
Trade: Grand Bahama - Andross - St.Martin - Antigua - Cat Island - San Juan
Combat: Charleston - Vera Cruz - Sisal - Caracas - Curaçao
Navigation: Port-au-Prince - Tortuga - St-Augustine - Turk Island - Tampa - Fort Carolina - Santa Domingo
Ship building: Port Royale - Barbados - Gibera - Nombre de Dios - Trinidad - Guadeloupe - Havana
Visibilty Range: Cayman - Margarita - Roatan - Port of Spain - Belize - Puerto Santo