Yup, it's in Dungeonscape.
I'm playing one in the only remaining 3e game I'm involved in at present... it's a fun class to play, though I'm definitely doing it warlord style and the game is very non-RAW and even, dare I say, idiosyncratic.
You can really see some seminal 4e stuff in that book, regarding per encounters (in the factotum) and the 4e trap and encounter design philosophy, including the introduction of monster roles. It's a very good book that I strongly underrated until I really got into playing with some of the rules; the encounter trap stuff is especially strong imho.