The main article says, "bulk traders" sell jade.
I tried this by calling 2 bulk traders from different tribals. None sold or purchased jade. I also tried a tribal shaman trader. Same result.
The main article says, jade drops from tribal raiders. I confirm this. I will try now an outlander bulk trader and an outlander exotic goods trader.
I must add that my game is obviously corrupted by a hacker. He also influences trade. One time settlements sell the same goods after reloading the savegame; the other time they sell other goods. Keep in mind that clicking on the settlements shows if they have restocked after last visit. So, it seems originally the game is intended not to be cheated by spam reloading for trading.