Or you could go for a dual-threat that you won't reveal as such until later on down the road.
Have a city-crushing horror summoned that your party will (hopefully) just barely defeat, but have that as smokescreen for your bad guys TRUE motivation. And have that motivation be something like the monster from Harry Connolly's Child of Fire. Basically, the main enemy/family had summoned an Outsider some time ago and enslaved in a special band/thing and used it for information and power. It spent a few generations breaking free. Then bad stuff started happening.
So, there you'd have a dual-threat with levels of import. First, the city-crushing horror which gives you a suitable finale vibe and the bad guy being Smarter Than That and using said finale as a set-up for bigger and worser things, for an added heaping of This Is What Happens When You Don't Do What Rashid Says.
Also: My brief summary of Child of Fire does it no justice. Read the book. It's awesome. Best stuff I've read this year.
I think that were there such an analogue then someone (Ivy, Kincaid, Luccio... someone) would have mentioned them at some point. At least they'd have been given an off-hand reference in a book like Changes.
Unless you consider Monoc Securities to be such a group?