The rare Kaumo spear? Yeah, With my PC, I've gone through every Kaumo village and found but one spear! As for finding items within the 'wrong' culture, I just assume they traded for it at some time. How else would they have the various Masterwork items?
Probably they have traded it, but I have found only 6 skramasaski total in five years (two in Kaumo, four in Sartola), so there's is a question who has sold it to them? Because the supposed producers have it mostly out of stock...
For comparison, northern bows are extremely frequent in Kuikka villages (and other northern, but Kuikka have sometimes even 7 northbows in a single kota, and I expect to find one masterwork quality every three villages on average). And yet, no southerners seem to have it - ever. So the trade seems to be wonky. OR the villagers are filthy bandits in disguise, and they killed some adventurer and brought his stuff home. That would explain my encounters with kaumo robbers (which are more frequent than in other cultures).
As for kaumo spear, I haven't see it at all on the ground. But some villagers have it in inventory, and some of these want to sell it. They have only standard quality, though, so given how unhandy it is it's not worth it. I bought one as a souvenir.
Nah, it's not a bug, skramasaksi can appear among Kaumo as well - although rarely, as other "war" weapons. Wealthy village it must have been. And there are of course little chances of some "non-cultural" items to find their ways to unexpected places as well.
I don't know, Driik seem to be generally more wealthy. Though Kaumo have many, many clothes and armours, they usually are in rough quality so not that valuable.