You can defeating enemies in the forest next to the castle will drop items. let me know the result then
I managed to get it this way, but I don't know during which fight. I did several fights but each time it didn't give me it in the list of items received. It was later when I looked at my inventory that I saw that it was there.
So, you figured it out yourself — that's great! The item drops are random. 😄 Glad you finally got it! :3