I'd do +2 total. 1 for availibility, 1 for knowledge. You only get +1 for knowledge with Faeries anyways. Besides, it should be harder to know then just throwing steel shot at them. Not a +0, but not a +2 either.
Actually, I run it that "cold iron" is a +4 Catch. It's common and any respectable Paranet member knows to grab iron to put paid to faeries. It really doesn't make sense to say that it requires special knowledge.
For a godly scion, a brawler in the style of Hercules, we designed a catch called Mortal Women. He gets +2 for them being so common, and +1 for the fact that experts in the study of the sons of gods would know about their being toppled by women. It's not something you need to know him personally for. Here's the relevant text:
"If almost anyone with an
awareness of the supernatural knows about the Catch or could easily find out, you get a +2.
"If knowledge of the Catch requires access to
specific research material that could be restricted, you get a +1.
"If knowledge of the Catch requires
knowing you personally to learn about it, you get nothing."