Where do I get the asmodian armor skins?

shoes, gloves & pauldrons in Eracus Temple.

You can buy these armorsets from a shugo marked with a dot on the map in Eracus Temple at night game time.




chest & leggings around the Lepharist Citadel area.
The second shugo Chicorinerk in Lepharist Citadel spawns on the 2nd, 19th and 28th of the month from 1am - 4am and on the 6th, 10th, 14th and 23rd of the month from 12pm - 4pm. Once again, this is game time.






Level 50 Armor

The NPC is in Theobomos Lab (bottom left corner) and you need to be at least level 46 to enter. There are multiple locked doors before you can reach the NPC's location, and you get the keys from the (level 49-50) elite monsters inside. The NPC can spawn in 3 possible rooms, but is not always there. It has a very low chance to spawn in any of them, so this is not a very easy set to get.