Seriously, Monsters didn't drop them last I played, and I keep forgetting about them.
Like, I just did a Screaming Bell; killed a Spawn, realized I forgot the dice right as I droped down to the next area. Ah, well, at least I'll get the one on the rat-ogre at the end.... nope. Forgot it too, after spending the second half of the map thinking about it. I'd be ok with just a message everytime you kill a Monster, "DON'T FORGET THE BLOODY DICE"...