You buy it.
Joseph Stalin VS Richard Nixon
It's part of the character, he only gave high-fives with the iron hand.
The Covenant first attack Harvest, that being the reason the book is called "Contact Harvest" This would have to be shortly there after as they didn't declassify the attack on Harvest right away, and the trainees are still training for the Insurrectionist conflict. This will be one of the first (not THE first) instances the Covenant has attacked a human colony/military complex.
The one in the new movies is the most recognizable, and more closely related to Norse craftsmanship, though the one made for the Thor cartoon with an axe head on one side might be easier to craft into a boomerang. Personally I think the more squared off current iteration would be the way to go if you could make that one fly, maybe even incorporate the leather strap into the design to give it the right shape. Though I have no idea how to craft a boomerang and thus not sure what would help it fly.
Pretty amazing stuff my friend.
We're running late on episode 4 due to several unforeseen issues. We are working to resume our series very soon. Please bear with us.