I have seen the PLD Tidal Wave Shield twice just after that patch when they started dropping.
Never saw one again on more than 1 month.

I have never ever seen the WHM Tidal Wave Buckler, nor the Mirrors (of course).
I have farmed Leviathan over 100 times by now.

So I can say that the REAL drop rate of the mirrors is 1% or less, which is absolutely ridiculous.