Farm up a few hundred scraps and play the “Create lottery” with your blacksmith, if you are the right level for the weapon it has a chance to roll a good one of that level.
Could take like 500 scraps or more though, easy enough to farm mind.
All mobs of the same rank and level have the same loot table, with the exception of Monster Infrequent rare items and components. None of the items you’re looking for are MI’s so there’s no place in particular to go looking for them. Kill monsters and take their stuff.
If you want better loot, kill higher rank monsters on harder difficulty levels:
ultimate > elite > veteran > normal
nemesis > boss > hero> champion