Where can I find info on the Red Mantis?

[Eyebreaker]

I apologize if this is in the wrong place. I didn't see anything else that looked like it should be there instead.
Which book can I find info on the Red Mantis?

[Eelario]

PathfinderWiki entry on the Red Mantis

refer to the references cited therein...

[Patrick Harris @ SD]

Because you asked: Campaign Setting forum

[Severed Ronin]

If you're looking for books and/or PDFs that talk of them, you should be able to check out the Faction Guide as well as the Inner Sea World Guide. Both have a couple pages dedicated to the Red Mantis Assassins.

[Liz Courts]

Moved thread, fixed URL links.

[Kajehase]

The best source for Red Mantis information is probably Pathfinder #9: Escape from Old Korvosa, which has an article about them.

In addition to what's already been mentioned upthread, you might also be able to find some tidbits in the Ilizmagorti entry of Cities of Golarion

[Thanael]

Cities of Golarion describes the city of Ilizmagorti on Mediogalti Island.