Blowguns have a few complications to them. First is that you need wood that is hollow or easy to make hollow for the blowgun and these characteristics are not common in the world, aside from bamboo, most plants like this are found in the tropics. While blowguns are pretty simple, the darts for them are less so and can be complicated to perfect. The aspect of blowguns that are even harder to invent/develop is the poison. Many blowgun poisons are a mixture of many different plant and animal chemicals (including 3 different beetle larva as part of a particular poison). This would take a lot of experimentation to figure out.

Also I'd like to point out that blowguns, darts and poison are unlikely survive in the archaeological record and this is especially true for the tropics because of the insanely high decomposition rate. You may also get more info from r/askanthropolgy