Any of the minibosses that drop Scraps for you when you kill and loot them have a big chance of dropping these for you - just not all the time, if you aren't lucky, since Scraps aren't a common resource and don't have a 100% chance of dropping from enemies. Once you kill a miniboss, move away from the camp it spawns at and return later for a chance of obtaining more Scraps from that miniboss. Eventually, you'll get some Scraps to smelt inside a Furnace in exchange for a small amount of Eldarium.