Well, there are no wads, so you wont be finding any. VERC has a big list of information about the SDK including what Materials are. A link to it is on all the sites including HL2.net's news page and on steampowered.
I thought we could still use wads for CS:S maps. Like extracting the .wad from the counter-strike 1.6 gcf file and then add them in the new Hammer and use them... Are you sure we can't do that? I don't buy HL2 from Steam so I can't test right now...
Well in the new Hammer, you can add in Materials and Wads. But just because Hammer still supports Wads doesn't mean that Valve is using Wads in HL2 and CSS.