How can I hunt a Teostra?

After defeating a Teostra, which was an objective for a post game sidequest, I decided that I want a Teostra hammer because it’s the perfect fit for the strategy I’m creating. However, I didn’t get enough monster parts to do so and am required to slay another Teostra if I want to forge one.

The problem is that these guys are incredibly rare and I have no clue how I’m supposed to look for one. What’s the best way to go about this?