As nice as it would be to have a full set of Myrosian, the Helm does not exist...yet .
The Legion Leggings however, do exist, and can be found in the Mercian Royal Crypt. I'm pretty sure I found them in the farthest-side sarcophagi. So you have to prove yourself by making it all the way around...or you can skip the other rooms to get there .
Using Ruby Keys and defeating them bosses can net you some yummy rewards. Surviving the initial wraith ambush to enter the Crypt...best of luck surviving there~
They do spawn in the mercian crypt as mentioned above, however they are not a guaranteed spawn. They have a small chance of spawning in certain containers in the mercian crypt. You may get them first try, or you may have to farm the crypt several times. Best of luck.