Over on National Geographic, there is a nice little description of duelling with shark-tooted clubs.
Check it out - scroll down to "
"Armed to the Teeth."
"The main bodies of the weapons were made of wood, and shark teeth were painstakingly sewn along their edges using thread made from coconut fiber and human hair. Because the islanders had no metal, they used spiral snail shells to bore holes in the teeth before sewing them to the weapons.
[. . .]
Often in these battles, two "champions" would fight in a central skirmish. The champions "were dressed in this really cool armor made of very tightly woven coconut cords, and they had tiger shark 'brass knuckles' and helmets made out of dried pufferfish with spikes on them," Drew said."
Pretty fun stuff, eh?
How would you represent this kind of weaponry in GURPS? Easily. The Polynesian shark-toothed club, the tebutje, is in Low-Tech on page 62. Spoiler - it's treated as a bone macuahuitl, which is also in there. Both are shark ridge-like edged material studding a club.
The spears? Bone-tipped barbed long spears or pikes will do the trick. The bone and long spear bits are in Low-Tech, barbed is easily added using the options in LTC2.
The multi-shafted clubs? Just increase the cost and weight of the tebutje. It won't do much to make it a better weapon, though, but it might increase you chances of hitting (say, by reducing Dodge by 1) but it would also be easier to parry (+1) and probably a bit difficult to use (-2 for a top-heavy weapon). You could add +1 damage for the extra weight, if you're so inclined. Most crazy weapons are like that - look cool, but the added doodads make them less handy and less effective even if they're more intimidating looking.
The armor? Easily treated as cane armor or horn armor (also in Low-Tech, this time on page 106). The helmet is trickier, but treating it as spiked cane isn't a bad option.
The rules? Simple - follow the ones in the article, make sure you use the rules for shooting into close combat (for the thrown clubs), prime up on the rules for long weapons reaching over allies, and let people Sacrificial Parry all over the place. And use the Tournament rules to pace it out, because in this kind of match you'd expect a fair amount of clash-and-stop and probably some rules for when it ends.
I know from experience, it can be real fun to throw a ritual duel like this at PCs, since they're likely to be more badass than the local champion, but much less well prepared to fight with the unusual weapons. It because badassitude vs. experience. If they haven't seen this kind of thing before, a quick look at the First Encounter With a New Way to Die box on Low-Tech page 60 will help here too.