Drake Hollow

Raid Bait is crafted under Curio Crafting, needing 2 black powder ingredients, which as of this guide, are rare. I tried to craft one of these once I started chapter 4 and didn't get a single drop through the whole map. It is best to craft this when at early levels and when raids do not have Terminers which will slow things down. You only need to craft one of these as you can revert back to your old save each time (right before you use it). What these do is start a raid at the base instantly, so make sure you throw this at the base. If the raid counter has already started, this will not count as enemies so make sure at the raid counter is not present. Throw the bait and kill the enemies so new waves spawn. Once the raid is over, quit without saving, then load the previous save and repeat. This was done in single player.

Here's a big tip. I recommend doing this in sandbox mode. The reason being is that the higher level camp you have, you higher the number of enemies will spawn in on a raid. I was at a camp level 12 and I got around 22 enemies instead of the usual 12. As for black powder, there are a few places I saw them drop.
The most common is after you destroy all the vines on an island the chest spawns in and has a small chance of dropping there.
Another spot is destroying those big creatures with an eye at their torso. Their drop rate is low as well but they do drop occasionally.
Lastly, I noticed that secret chests that are in those half-submerged churches dropped black powder a few times as well. It took me 6-7 hours of a sandbox game to get over 100 enemies to raid.