I've been reading some of these posts, and there's talk of even legendary rarity.
So far i've gotten 5 masterwork weapons (I've collected at minimum 12 of some, over 30 insult and injury (once got 4 of this one in one expedition))
I've had about 4 masterwork components show up.
How many are there supposed to be, I would think they should have enough for each different epic, but i could be wrong. If there is more, RNG must be seriously broken
I was able to find an Article that mentions all the Masterworks: https://www.rockpapershotgun.com/2019/03/11/anthem-masterwork-all-the-legendary-weapons-components-a...
There are Legendaries as well, but those obviously drop less frequently due to being the highest Rarity.
However, they have more of a chance to drop in Grandmaster 2 and 3, so I've heard.