I've entertained the thought before too, but my wallet said no
may you be able to complete this vast endeavor. Maybe start in a small area?
well here's a list for thought... some of these may not apply
Qin Chinese sword
Da Dao
Taiwanese aboriginal blades (in Atayal it is called Laraw)
Bontoc/Kalinga/Ifugao Ax, etc.
Panabas
Mandau / Parang Ihlang
Sumpitan
Papua New Guinean bows and arrows, adz/ax
Pacific island (Vanatu?) garrotes and clubs?
WW2 American soldiers' arms (Japanese heads)
WW2 Japanese solder's arms (other people's heads)
Aztec axes and macuahuitl
Central and South American blowguns?
Chilean Corvo
Congo "execution" swords?
Celtic swords/axes
Guillotine
some of these were surely great choppers of necks but...
not necessarily part of a ritualized, male, violent pseudo-predatory combative role in society.
some of these are examples of head-taking as trophies of war, or as part of executions