5% chance you'ld be so unlucky, with misfortune 1, over 150 turns.
edit: more specifically, each turn you have a .98 chance of not getting a hero. after 150 turns the chance of not getting a hero is (.98)^150=.048296...
Aikamun, you've just been supremely unlucky. In test games I've run, I've received national heroes for all nations. Sometimes things just work out that way. Much the same as the odds of having two starspawn priests get feebleminded by the Void Gate within the first 20 turns, it's just a bad run of luck.