I've spent almost the same time you have (probably somewhere right around four hours) and have zero Black Hole drops to show for vs your four drops.
Seriously, what the hell. I'm just hoping it's because of the Zaford event and some weird coding and not incomprehensibly bad luck. --- "If you come here, you'll find me...I promise..." ~Squall Leonhart "Tonight's the night we silence you, there's nowhere left to run." ~ADTR