Yeah you can get weapon specific mods, you need a modable weapon and it needs to be an energy weapon from what I've been told, so it kinda stuns them rather than kill them.
Right now I'm in act 1 and I know that if I go into the flathead mission you're forced into an encounter where you're in combat with Dum Dum who is the kinda right hand man of that gang. There's various ways of actually going through that mission as I've tried various scenarios that change the outcome but they all result in some kind of combat where you're shoved out in the open in front of enemies who are blasting you, so you need to shoot back but I can't.
In my first play through before I restarted to respec my character I deffo did get that eye mod at some point shortly after you get the eye implant, and so did my friend on his play through, so it makes me think you can pick it up somewhere I'm just not sure where. There doesn't appear to be vendors that I can find that will sell you implant mods, you can goto ripperdocs to get brand new implants but not the mods you slot into the implants it seems. Nor can I seem to craft them, or see anything in the upgrade trees that allows crafting of implant mods.
Anyone got any ideas? Is there other non-leathal weapons that'll beat Dum Dum in a fight, I'm considering just brawling with him but I'm not sure if you defeat an enemy with fists it actually kills them or wounds? Jackie is with you in that area and will kill the other normal mobs for you but for some reason if you leave him to fight Dum Dum he doesn't do any damage to him, i guess because Dum Dum is basically a special NPC.