While you can still get the tabards from Argent Tournament vendors on the beta, each major city also has a faction quartermaster (usually close to the city's flight master and introduced in beta build 13066 in late September, I think) selling both the tabard and a set of level 40 cloaks. The tabards are available at friendly for 8 silver (even at the Tournament -- they no longer require Champion's Seals), but you can't get the cloaks without being exalted. Still, grinding reputation for one of your faction's races should be considerably easier in Cataclysm -- all you'll have to do is get to friendly, buy a tabard and run dungeons as you normally would.
This is a great addition to the game. Not only will you have access to cool tabards even at a low level, but it should make getting other races' mounts and faction discounts much easier as well.