Like in topic, guys that are online seem not really helpful about the matter.
I got one from the Large Kepa boss fight and another one by killing regular Kepas.
Regular Kepas drop them I think. I even got two. Sold the extra one to NPC though. Sorry bud, would have given it to you for free.
Yes, they are dropped by Kepa afaik with a 1.5% chance. You can see it here: http://www.tosbase.com/database/items/628054/
I found three of them in the period of testing