Keep in mind that villages' inventories slowly refresh with time, so it may be worth going back to Driik or in villages you've already visited to see if they have interesting new things to buy.
I have visited driik 5 times. once a year. I just explored Kaumo again, but there is still no hunting horn. Should I buy all of their products?
I was about to start a new thread on Hunting Horns
in vanilla game but then found this older thread & question and decided to revive it instead.
To answer your question
looks like one have two routes to obtaining a hunting horn in the vanilla game:
a) either by going to Sartola (rather than Driik) lands and checking villagers and items for sale on the ground inside buildings,
b) or alternatively by attacking a Njerp camp.Obviously no item spawn is 'guaranteed' so one may not get lucky initially, need to keep trying...
Here is my first hand experience: after not seeing a single one of these semi-mythical tools, in the last week I found two.
1) One was a new character/game that just visited 3 Sartola villages and found one!
2) The other character was also a brand new one, while testing Runaway Slave scenario, I rolled about 26 characters, but only a handful of them actually killed/looted Njerps (rest just took the flight option) and one of the Njerps in the camp had a hunting horn on him!
These finds both occurred on game version 3.70beta although hunting horn availability does not seem to be a recent change as the only mention to hunting horn in news.txt is on line number 14931 for an entry from version: 2.08, released: Jul-31-1995.
After finding two hunting horns in a week and thus confirming with my own eyes that it still exists/spawns in the game, I did a quick wiki & web search and did not find anything on the official wiki on this particular item but I did find a page on the unofficial wiki which says exactly the above (i.e.: obtain from Sartola or Njerp camp).
I hope emboldened bits help other seekers of hunting horns.