Finding enough of these to get both uchigatana and nagakiba to +18 before Morgott is one of the most tedious parts of the game.

Just a note that could be updated, the 'grotesque creature' in the Grand Cloister is an Ulcerated Tree Spirit, and a mean one with all the rot.

Game genuinely suffers from not dropping enough of these mid-playthrough. You are stuck using two weapons tops for the vast majority of the game until Mountaintops onwards has a clearance sale on smithing stone 7 lying around.

Also the fallingstar beast out of lyndell drop 5x of [6]

Are those inside the breakable statue near hermit village definitely no.6?

I have access to the royal capital and mohgwyn's palace, so there are no enemies to farm who drop this stone, even if its only a very small chance to drop?

You can find a total of (3) in Mohgwyn's palace. One in a cave, one in front of a bird where white mask invader's are, and one on the road up to palace-ledge approach road.

You can effectively be at +17 with one weapon before fighting Radahn without going to Altus Plateau

found one just north of the palace approache ledge road. Just go north, and turn left after the first big stone. it's there in front of the stone

3x in statue break with runebear in hermit village