just play through it again, it's really hard to miss the majority of them. you just have to observe your surroundings. like here's some that are easy to miss.(keep in mind the gunpowders are randomly generated, they're always in the same main areas, but obviously the gunpowder isn't going to be everywhere you go.) the diner where you encounter tyrant and can either run underground or run behind the kitchen and blow him to ****.(you have to fight him pretty much either way.) you can enter from the back (the alley with the save room) or you can enter through the front (up the street close to where you switch the indigo plates to get the battery). if you enter through the back you never really have to look around the diner, but if you enter through the front you'll notice there is a little area to the right that leads you up by some tables. sometimes there is gunpowder there, sometimes it's on the tables to the left. sometimes it's on both. so just be a bit more adventurous, but be advised being adventurous is dangerous so always go prepared.