Fabulous Free Market Deals

They're mistaken, there's no familiar other than Wolf Underling linked to the +100% Item Drop Everywhere effect, at least not in gMS.

I've only seen one in Windia for sale and that was a while ago. Both of the ones I own came from the MTS (for 2.7k each), but I used the one on my Demon Slayer before they were perma. L> Familiar Revive Item =[

As for whether not it drops, I would think so. I've hunted myself for a few hours before I got bored on 8x, but I also got nothing, but Red Stirges drop their familiars, and you're not even supposed to be able to kill them, so I don't see why Wolf Underlings wouldn't, I think it's just that it's a higher leveled monster, so it wouldn't drop familiars as often.

I dont think it has anything to do with level.
From my experience, some quest monsters do not drop their respective familiars.
Such as the puppet from the resistance quests from francis' room. I spent 20 hours in there and got nothing. They're level 66.

Considering i have yet to hear of anyone who got large multipliers and spent longer hours there have it pay off, i find it safe to assume it is not in the drop table.