In a lockbox outside the Mysterious Hill Home point of interest up in Grizzlies East, just northeast of Bacchus Station.

Or you could get it from a fence

At the begining if my game I went to the febce and bought everything,but i dont gave it

I think you have to progress further.

👀I’m in the epilogue👀

Then I don't know what to tell you.

That's how I got the poison arrow crafting.