Arcane Magical Writings are one of the items needed to restore the Weapon sets in RD. While there are many things needed, it turns out this is one of the major barriers because it takes so many, and they are so slow to gather.
Needed 105 for the set of Main hand, Offhand.
How to get them, listed by what I think of as the order of difficulty:
Auction House: As of this date they go run about 8k. At 840k to buy them all, this is cheaper than it once was, but still fairly pricey. ..but its quick and easy.
Heroic Encounter's: These are easy to do as there are usually many people gathering to do them. Problem is you don't get an AMW (arcane magical writing) for every HE. It seems to be about 1 in 4 for me. This can take a lot of time, and if you're contributing to the main ship HE, a lot of resources. Bonus with the Ship HE, about 1-2 times per day you can get 2 AMW in 1 fight. Dont neglect the small Hes in this. They can go fast, especially with a group, or a HDPS character.
Treasure maps: The maps you get from digsites are good to keep and run all at once, or as you see them in your normal path. Very rarely you can get a AMW out of these. I wouldn't even expect more than 1 in 20. The resources gathered however will help you in the next strategies.
Secure the district:
This one can be hard to find info on so far. You find it in the top right corner of your Cloaked Ascendancy campaign window. This one has a lot of details to make it efficient, but is the fastest and cheapest route to AMW.
Each time you fill SD (Secure the District) you get 1 AMW. Fill it by:
The travelling merchant: This step doesn't get you AMW directly, but does speed up donating to the guardposts. You'll find that lots of donations eats mostly 1 resource, reclaimed weapons. It can be found at the left hand dock at the top left of the map in RD. Several docks down from where the ship HE is.