Two reasons they are so diffcult to farm is obviously the explosions are no fun and also most afflicted groups contain a "party". By this i mean, they arent all melee based or caster based but a mix of both. Mixed groups tend to be more difficult than uniformed groups.
There are smaller groups (of three) of afflicted right outside of Zin Ku Corridor that are a bit more manageable than the massive groups that tend to run into each other in the Undercity, etc.
Those groups very rarely have a Ritualist or Monk with them, which makes them a bit easier to manage if you're looking for an easy Afflicted target.
These weapons look really cool! However they are pretty difficult to get. I got a perfect focus item once from a chest. My advise: just run the missions and through areas with as few people/henchies/heroes as possible. Just bring lots of
keys and hope like heck.
Afflicted are ridiculously hard to farm. They have more enchantment removal than the rest of Factions put together (probably Prophecies too). They also specialise in massive amounts of degen and conditions like Dazed and Blind. Not to mention they explode upon death. Ritualists have a 0 recharge 4s cast ressurect and powerful healing. Monks are anti-conditions, spam RoF and maintain Retribution which can annoy warriors on top of the rest.
They're extremely good at pressure and can spike very well too. Traps or Shadow Form is really the only way to farm them. You could always just run around with the E/A Sliver Armour build and kill off a load off loads of them near the Constructs in Sunjuing explorable.