I know how to obtain the normal version, but I have no clue how to get a Proof of a Concord Well Kept to drop for me in any way. How do I get one? I know that killing an invading dark spirit when summoned to another world as a Blue Sentinel or a Blade of the Darkmoon will get me one, but how do I obtain a Well Kept Proof from a standard summoning?
The only way to get a Proof of a Concord Well Kept, according to the wiki page is to be summoned as a Blade of the Darkmoon and then kill an invading dark spirit that is a member of Rosaria's Fingers. This item is not dropped any other way. In fact, the wiki dispels a misconception that people have about where to get this item:
It is a common misconception that these drop from Aldrich Faithfuls after killing them. However, this is not the case, even if the player lands the killing blow on them.