Getting ready for monster book...

The PQ monsters are in the book (as shown by Isaac's screenie of King Slime and Alishar among others). In kMS, I believe, you could trade in the Maple Leaves for the various cards. Papulatus was...10k leaves per card, IIRC based on what Isaac said. The leaves had around a 95% droprate there as well, so you could find a lot of them easily.

Now that you mention, and for no particular reason, I'd love to find a list of their prices...