Fallout 4 Guide: How To Find Grognaks Axe and Costume

Intrepid star of his own series of comics, Grognak is more than just a barbarian: he's the character who at the cusp of the Great War starred in a debut TV show based on the comics, the props for which you can find in Hubris Comics, a small shop in the Boston area where apparenly they were filming the new program.

Grognak's Axe is locked under glass when you walk through the front door, behind some cash registers. It causes more stagger to your enemies and additional bleed damage.

Upstairs on a shelf amid some other props is Grognak's Costume, which provides +2 to STR and additional melee damage. 

For another great unique melee weapon be sure to hunt down the Kremvh's Tooth.