It seems Page 16 (Potshot) and Page 15 (Conspiracy) symbols can be bought over Armas, although I'm not too sure if it's account bound since I've never bought them myself. However, Page 13, 14, 17, 18 seems to be unlock able through certain game events that run one time per year. The problem is some people don't have the time to go through all their characters if they choose to unlock every single page of symbols before the event ends. These pages don't seem to be purchasable through Armas either. Another issue would be that some symbols are made on different characters and can only be editable through that one character instead of the account itself. There should be a way to unlock these pages account wide since not everyone has the time to go through the events all year round.