So for some reason most guides and posts online are saying that in order to have Senor Hilter appear you need to finish the focus Guardia National before Germany capitulates. This is NOT true.
You need to complete the focus Work with the Nationalists before they surrender. Shortly after the focus you get an event titled "strange visitor" and if you select "what could go wrong" you instantly become fascist Argentina with Senor Hilter as the leader and the achievement pops. Best to do Non Historical and keep restarting until Germany has a civil war. He appeared before they even finished the civil war.
Berlin has to fall before he appears. Germany doesnt have to surrender.