Kerry Hampton also uses A2 a lot. Most of Bailey Bradshaw's are 52100, CPM 3V, carbon damascus, etc. Don Hanson's will normally be either W2 or carbon damascus (he's said most of those he made in the 1990's were O1). Chris Crawford does almost all of his in O1.
Lots of custom slips have D2 (though that's kinda pushing it as "carbon steel" -- however, it's not stainless either, especially since not very much of the chromium content is free).
I make liner locks instead of slipjoints, no matter, but I started using O-1 because it was readily available in ground flat stock, very inexpensive, easy to grind and heat treat. Now after a few knives I still mix in O-1 with other blade steels. Dan