That Castle Tactics whatever skill reminds me of the hassle I went through to get the 8th page of Arrow Revolver in Mabinogi.
Most of the other pages (10 in total) were so easy to get that I was throwing away copies of them. 3 of them were difficult to get, but I still had multiple copies of 2 of those pages.
The 8th page was a rare drop from the boss of a specific dungeon with a specific ticket that was pretty much impossible to solo without god-tier reflexes (which I don't have). It took me over a year to get that page, and even then I was only able to do the damned dungeon about 5 times in that year due to the trouble of getting a random party together of competent players to help me.
So yeah... some archery skills can have downright horrid conditions on procuring them.