it's all random. farm core of arreat over and over.. you'll find some set pieces. most of the time, legendaries are better than set pieces anyways. unless you want 4 piece tal rasha
This will be the whole problem with RoS, drops will still suck and gear sets.
The AH was bad, but at less you could gear your toon. I don't mind at leas buying gold from a third party and spending on the AH.