so i went to my neighbours to check out if it really is such a big problem.
first village, the one i live next to less then 3 km distance, a bloody masterwork kaumo spear!
i guess it all comes down to luck.
i do recall getting both my northern spear and my previous kaumo spear from robbers, in cultural lands they often have the culture of that region, and with that come the weapons of that region.
as always, i find you should not worry to much about wich particular weapon you use, you'll come across a suitable spear sooner or later. and a decent kaumo spear is still decent enough, it's mostly skill anyway.