What does an old player need to do to find his Grimoire?

Started to play Destiny 1 again. Been having fun with the nostalgia and even managed to get some raid teams together. One of things on my list of things to do while back was to try and max out my Grimoire score. It is currently at 5360 or so? maybe it was 5260? Either way, I knew I was CLOSE but not there...so I started searching for ways to see what I have and what I do not...and I cant find jack shit. Anyone know what I can do to scratch this lore itch? Or do I gotta give up?