Searching Amazon, you find Plame the Flame's book, "Germ" Although a lot of the info supplied to her was from Chalabi, I'd wager that she got a lot of stuff from her contacts in the CIA WMD division. Namely, PLAME. I'm sure they've known each other for years. That's why Miller wanted her questions and testimony to be very limited. I was really surprised when Fitz agreed.
Miller had an idea who Plame was, but not her name. She got all of her stuff from the CIA through an intermediary.