Arkaïl's Armor ranges from each chapter. The start off armor is the Gladiator's armor set which you can obtain by challenging the members of The Black Hand.
The second set you can get in the same chapter is the champions set. This set can be found through searching and looting throughout the 1st chapter (could be wrong about chapters cause i play the pc version) or just the same chapter as The Black Hand.
The 4 available Armor sets are: