I've set the item drop rate to 25% if you don't have it. Not every item drops from every enemy, so to find out which enemy drops the item you're missing, click the ? icon on that enemy. This will show you which items it has a chance to drop. If you kill 4 to 5 of that enemy, the item should drop. I also boosted the player's base stats so you can kill enemies faster even without the items.
If you're struggling to clear enemies without the item, you can reset your stats and invest more points into STR and END. Also, if you buy a lot of clean money auto upgrades, you'll log in the next day to find a decent amount of money stacked up, which you can use to buy stat points and significantly strengthen your character for the early game.
Once you've done all of this, you shouldn't have any trouble getting the item to drop. On top of that, the money you earn from killing enemies is proportional to your auto income, so you'll be able to clear Dungeon 1 quickly.