for both Tough wood & Leatherskin go outside to Rocky Mountain and it's one of the "clickable" random drops from the wooden crates, not the ores or monsters.
I don't know if you have the same problem, but I play on android so when I collect the drops from wooden crates, the "notification" of what you collected is shown out out of bounds since the placement is at the edge of my screen. You can check your inventory afterwards, or collect the drops one at a time and make your character run towards the center so can see the character's overhead notif before it fades away lollll