So far I'm on chapter 5, and have 4 royal arms, all of which I have found during the course of the main quest. I looked at the display of the royal weapons on the menu and there is a gap between the ones I have found so far.
This led me to believe that I have missed one that I should have found by this point in the story, but I haven't seen a quest for it (optional or main).
I also visited a royal tomb without a related quest, and found only a note from some hunters saying that it had been stolen, which leads me to believe that there will be a quest to retrieve it at some point.
So will I encounter each of the royal arms through the main questline, or can some be found without a related quest?
Please put any spoilers for beyond Chapter 5 in spoiler tags.